Systems and methods for gslb based on ssl vpn users

ABSTRACT

The present invention provides a system and a method for global server load balancing of a plurality of sites based on a number of Secure Socket Layer Virtual Private Network (SSL VPN) users. The SSL VPN users may access servers at each of the plurality of sites. A global server load balancing virtual server (GSLB) may receive a request to access a server. The GSLB virtual server may load balance a plurality of sites wherein each of the plurality of sites may further comprising a load balancing virtual server load balancing users accessing the server accessing servers via an SSL VPN session. GSLB may receive from a first load balancing virtual server at a first site, a first number of current SSL VPN users accessing servers from the first site via SSL VPN sessions. The GSLB may also receive from a second load balancing virtual server at a second site, a second number of current SSL VPN users of the users accessing servers from the second site via SSL VPN sessions. GSLB may determine to forward the request to one of the first load balancing virtual server of the first site or the second load balancing virtual server of the second site by load balancing SSL VPN users across the plurality of sites based on the first number of current SSL VPN users and the second number of current SSL VPN users.

RELATED APPLICATION

The present application claims priority to and is a continuation of U.S.Non-provisional application Ser. No. 12/323,153, entitled “Systems andMethods for GSLB Based on SSL VPN Users” and filed on Nov. 25, 2008,which is incorporated herein by reference in its entirety for allpurposes.

FIELD OF THE INVENTION

The present application generally relates to data communicationnetworks. In particular, the present invention relates to systems andmethods for load balancing network traffic across a plurality of sitesbased on SSL VPN users accessing the sites.

BACKGROUND OF THE INVENTION

A corporate or enterprise may deploy various services across a networkto serve users from many areas. A user may use a client machine torequest to access a service, such as a web server, provided by theenterprise. The enterprise in order to improve the access to thisservice may deploy multiple servers at various geographical locations inorder to expedite the access and meet the demand of users. Similarly,the enterprise may provide a plurality of server farms positioned at avariety of sites and including any number of servers capable ofprocessing the client's request. The enterprise may use a load balancerto manage network traffic across these servers, minimizing the networkcongestion and improving the service provided. Similarly, the enterprisemay also use a global server load balancer (GSLB) to manage access toeach of the load balancers at different sites and further help in evenlybalancing the network traffic across the enterprise servers.

Any number of users may access the enterprise using different types ofconnections. Some users may establish connections with servers via aSecure Socket Layer Virtual Private Network (SSL VPN). Other users mayestablish connections with servers using connection methods other thanSSL VPN. Different types of connections may use different resources ofthe enterprise. For example, SSL VPN connections may use differentresources of the enterprise than other types of connections.

BRIEF SUMMARY OF THE INVENTION

The present invention provides improvements to load balancing byproviding a load balancing solution that utilizes informationidentifying the number of users using SSL VPN sessions. As SSL VPN usersand SSL VPN sessions may use different resources than other types ofconnections and users, the solution described herein provides loadbalancing based on a number of SSL VPN users accessing resources. Adestination for an incoming request is determined based on SSL VPN usermetrics obtained by the GSLB. In this manner the GSLB can load balancenetwork traffic of the SSL VPN users across a plurality of sites.

In one aspect, the present invention relates to a method for globalserver load balancing of a plurality of sites based on a number ofSecure Socket Layer Virtual Private Network (SSL VPN) users. The SSL VPNusers may access servers at each of the plurality of sites. A globalserver load balancing virtual server (GSLB) may receive a request toaccess a server. The GSLB virtual server may load balance a plurality ofsites wherein each of the plurality of sites may further comprising aload balancing virtual server load balancing users accessing the serveraccessing servers via an SSL VPN session. GSLB may receive from a firstload balancing virtual server at a first site, a first number of currentSSL VPN users accessing servers from the first site via SSL VPNsessions. The GSLB may also receive from a second load balancing virtualserver at a second site, a second number of current SSL VPN users of theusers accessing servers from the second site via SSL VPN sessions. TheGSLB virtual server may determine to forward the request to one of thefirst load balancing virtual server of the first site or the second loadbalancing virtual server of the second site by load balancing SSL VPNusers across the plurality of sites based on the first number of currentSSL VPN users and the second number of current SSL VPN users.

In some embodiments, the GSLB virtual server of a first appliancereceives the request to access the server via a SSL VPN session. Inother embodiments, the first load balancing virtual server of a secondappliance determines the first number of current SSL VPN users accessingservers via the second appliance. In yet other embodiments, the secondload balancing virtual server of a third appliance determines the secondnumber of current SSL VPN users access servers via the third appliance.In some embodiments, the GSLB virtual server requests a number of SSLVPN users from the first load balancing virtual server via an SNMP(Simple Network Management Protocol) request. The number of SSL VPNusers may be identified via an object identifier. The first loadbalancing virtual server may update a value of an object identified bythe object identifier. In some embodiments, GSLB virtual server receivesthe first number of current SSL VPN users from the first load balancingvirtual server of a second appliance via a metric exchange protocolcommunicated between the first appliance and the second appliance. Infurther embodiments, GSLB virtual servers requests a number of SSL VPNusers from the second load balancing virtual server via an SNMP (SimpleNetwork Management Protocol) request. The number of SSL VPN users may beidentified via an object identifier. The second load balancing virtualserver may update a value of an object identified by the objectidentifier. The first virtual load balancer of the first appliance maydetermine the first number of SSL VPN users from all users accessing thefirst site via the first appliance. The second virtual load balancer ofa second appliance may determine the first number of SSL VPN users fromall users accessing the second site via the second appliance. In someembodiments, the GSLB determines a threshold of a maximum number of SSLVPN users for the first site has been reached and responsive to thedetermination, forwards the request to the second site. In otherembodiments, the GSLB virtual server determines that a threshold of amaximum number of SSL VPN users for the second site has been reached andresponsive to the determination, forwards the request to the first site.

In some embodiments, the GSLB virtual server determines to forward therequest to one of the first load balancing virtual server of the firstsite or the second load balancing virtual server of the second site byload balancing SSL VPN users across the plurality of sites incombination with any of the following load balancing methods: leastconnection, least response time, least bandwidth, least packets andround trip time.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent and better understood byreferring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment fora client to access a server via an appliance;

FIG. 1B is a block diagram of an embodiment of an environment fordelivering a computing environment from a server to a client via anappliance;

FIG. 1C is a block diagram of an embodiment of an environment fordelivering a computing environment from a server to a client via anetwork;

FIGS. 1D and 1F are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance forprocessing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of an appliance foroptimizing, accelerating, load-balancing and routing communicationsbetween a client and a server;

FIG. 3 is a block diagram of an embodiment of a client for communicatingwith a server via the appliance;

FIG. 4A is a block diagram of an embodiment of an appliance forcollecting metrics via a network management protocol and for determininga load of services based on user selected metrics;

FIG. 4B is a flow diagram of an embodiment of steps of a method forperforming load balancing based on user selected metrics in view of FIG.4B;

FIG. 5A is a block diagram of an embodiment of a network environment forperforming global server load balancing among heterogeneous devices;

FIG. 5B is a block diagram of an embodiment of an appliance performingserver load balancing among heterogeneous devices;

FIG. 5C is a flow diagram of an embodiment of steps of a method forGlobal Server Load Balancing among heterogeneous devices;

FIG. 6A is a block diagram of an embodiment of a system for loadbalancing of user requests using SSL VPN user information; and

FIG. 6B is a flow diagram of an embodiment of steps of a method forglobal server load balancing of a plurality of sites based on a numberof SSL VPN users accessing servers at each of the plurality sites.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of reading the description of the various embodiments ofthe present invention below, the following descriptions of the sectionsof the specification and their respective contents may be helpful:

-   -   Section A describes a network environment and computing        environment useful for practicing an embodiment of the present        invention;    -   Section B describes embodiments of a system and appliance        architecture for accelerating delivery of a computing        environment to a remote user;    -   Section C describes embodiments of a client agent for        accelerating communications between a client and a server;    -   Section D describes embodiments of systems and methods for load        balancing based on metrics selected by a user from appliance        determined metrics and/or metrics collected from a device via a        Simple Network Management Protocol; and    -   Section E describes embodiments of systems and methods for        global server load balancing among heterogeneous devices.    -   Section F describes global server load balancing based on SSL        VPN user information.

A. Network and Computing Environment

Prior to discussing the specifics of embodiments of the systems andmethods of an appliance and/or client, it may be helpful to discuss thenetwork and computing environments in which such embodiments may bedeployed. Referring now to FIG. 1A, an embodiment of a networkenvironment is depicted. In brief overview, the network environmentcomprises one or more clients 102 a-102 n (also generally referred to aslocal machine(s) 102, or client(s) 102) in communication with one ormore servers 106 a-106 n (also generally referred to as server(s) 106,or remote machine(s) 106) via one or more networks 104, 104′ (generallyreferred to as network 104). In some embodiments, a client 102communicates with a server 106 via an appliance 200.

Although FIG. 1A shows a network 104 and a network 104′ between theclients 102 and the servers 106, the clients 102 and the servers 106 maybe on the same network 104. The networks 104 and 104′ can be the sametype of network or different types of networks. The network 104 and/orthe network 104′ can be a local-area network (LAN), such as a companyIntranet, a metropolitan area network (MAN), or a wide area network(WAN), such as the Internet or the World Wide Web. In one embodiment,network 104′ may be a private network and network 104 may be a publicnetwork. In some embodiments, network 104 may be a private network andnetwork 104′ a public network. In another embodiment, networks 104 and104′ may both be private networks. In some embodiments, clients 102 maybe located at a branch office of a corporate enterprise communicatingvia a WAN connection over the network 104 to the servers 106 located ata corporate data center.

The network 104 and/or 104′ be any type and/or form of network and mayinclude any of the following: a point to point network, a broadcastnetwork, a wide area network, a local area network, a telecommunicationsnetwork, a data communication network, a computer network, an ATM(Asynchronous Transfer Mode) network, a SONET (Synchronous OpticalNetwork) network, a SDH (Synchronous Digital Hierarchy) network, awireless network and a wireline network. In some embodiments, thenetwork 104 may comprise a wireless link, such as an infrared channel orsatellite band. The topology of the network 104 and/or 104′ may be abus, star, or ring network topology. The network 104 and/or 104′ andnetwork topology may be of any such network or network topology as knownto those ordinarily skilled in the art capable of supporting theoperations described herein.

As shown in FIG. 1A, the appliance 200, which also may be referred to asan interface unit 200 or gateway 200, is shown between the networks 104and 104′. In some embodiments, the appliance 200 may be located onnetwork 104. For example, a branch office of a corporate enterprise maydeploy an appliance 200 at the branch office. In other embodiments, theappliance 200 may be located on network 104′. For example, an appliance200 may be located at a corporate data center. In yet anotherembodiment, a plurality of appliances 200 may be deployed on network104. In some embodiments, a plurality of appliances 200 may be deployedon network 104′. In one embodiment, a first appliance 200 communicateswith a second appliance 200′. In other embodiments, the appliance 200could be a part of any client 102 or server 106 on the same or differentnetwork 104,104′ as the client 102. One or more appliances 200 may belocated at any point in the network or network communications pathbetween a client 102 and a server 106.

In some embodiments, the appliance 200 comprises any of the networkdevices manufactured by Citrix Systems, Inc. of Ft. Lauderdale Fla.,referred to as Citrix NetScaler devices. In other embodiments, theappliance 200 includes any of the product embodiments referred to asWebAccelerator and BigIP manufactured by F5 Networks, Inc. of Seattle,Wash. In another embodiment, the appliance 205 includes any of the DXacceleration device platforms and/or the SSL VPN series of devices, suchas SA 700, SA 2000, SA 4000, and SA 6000 devices manufactured by JuniperNetworks, Inc. of Sunnyvale, Calif. In yet another embodiment, theappliance 200 includes any application acceleration and/or securityrelated appliances and/or software manufactured by Cisco Systems, Inc.of San Jose, Calif., such as the Cisco ACE Application Control EngineModule service software and network modules, and Cisco AVS SeriesApplication Velocity System.

In one embodiment, the system may include multiple, logically-groupedservers 106. In these embodiments, the logical group of servers may bereferred to as a server farm 38. In some of these embodiments, theserves 106 may be geographically dispersed. In some cases, a farm 38 maybe administered as a single entity. In other embodiments, the serverfarm 38 comprises a plurality of server farms 38. In one embodiment, theserver farm executes one or more applications on behalf of one or moreclients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more ofthe servers 106 can operate according to one type of operating systemplatform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond,Wash.), while one or more of the other servers 106 can operate onaccording to another type of operating system platform (e.g., Unix orLinux). The servers 106 of each farm 38 do not need to be physicallyproximate to another server 106 in the same farm 38. Thus, the group ofservers 106 logically grouped as a farm 38 may be interconnected using awide-area network (WAN) connection or medium-area network (MAN)connection. For example, a farm 38 may include servers 106 physicallylocated in different continents or different regions of a continent,country, state, city, campus, or room. Data transmission speeds betweenservers 106 in the farm 38 can be increased if the servers 106 areconnected using a local-area network (LAN) connection or some form ofdirect connection.

Servers 106 may be referred to as a file server, application server, webserver, proxy server, or gateway server. In some embodiments, a server106 may have the capacity to function as either an application server oras a master application server. In one embodiment, a server 106 mayinclude an Active Directory. The clients 102 may also be referred to asclient nodes or endpoints. In some embodiments, a client 102 has thecapacity to function as both a client node seeking access toapplications on a server and as an application server providing accessto hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In oneembodiment, the client 102 communicates directly with one of the servers106 in a farm 38. In another embodiment, the client 102 executes aprogram neighborhood application to communicate with a server 106 in afarm 38. In still another embodiment, the server 106 provides thefunctionality of a master node. In some embodiments, the client 102communicates with the server 106 in the farm 38 through a network 104.Over the network 104, the client 102 can, for example, request executionof various applications hosted by the servers 106 a-106 n in the farm 38and receive output of the results of the application execution fordisplay. In some embodiments, only the master node provides thefunctionality required to identify and provide address informationassociated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a webserver. In another embodiment, the server 106 a receives requests fromthe client 102, forwards the requests to a second server 106 b andresponds to the request by the client 102 with a response to the requestfrom the server 106 b. In still another embodiment, the server 106acquires an enumeration of applications available to the client 102 andaddress information associated with a server 106 hosting an applicationidentified by the enumeration of applications. In yet anotherembodiment, the server 106 presents the response to the request to theclient 102 using a web interface. In one embodiment, the client 102communicates directly with the server 106 to access the identifiedapplication. In another embodiment, the client 102 receives applicationoutput data, such as display data, generated by an execution of theidentified application on the server 106.

Referring now to FIG. 1B, an embodiment of a network environmentdeploying multiple appliances 200 is depicted. A first appliance 200 maybe deployed on a first network 104 and a second appliance 200′ on asecond network 104′. For example a corporate enterprise may deploy afirst appliance 200 at a branch office and a second appliance 200′ at adata center. In another embodiment, the first appliance 200 and secondappliance 200′ are deployed on the same network 104 or network 104. Forexample, a first appliance 200 may be deployed for a first server farm38, and a second appliance 200 may be deployed for a second server farm38′. In another example, a first appliance 200 may be deployed at afirst branch office while the second appliance 200′ is deployed at asecond branch office'. In some embodiments, the first appliance 200 andsecond appliance 200′work in cooperation or in conjunction with eachother to accelerate network traffic or the delivery of application anddata between a client and a server

Referring now to FIG. 1C, another embodiment of a network environmentdeploying the appliance 200 with one or more other types of appliances,such as between one or more WAN optimization appliance 205, 205′ isdepicted. For example a first WAN optimization appliance 205 is shownbetween networks 104 and 104′ and s second WAN optimization appliance205′ may be deployed between the appliance 200 and one or more servers106. By way of example, a corporate enterprise may deploy a first WANoptimization appliance 205 at a branch office and a second WANoptimization appliance 205′ at a data center. In some embodiments, theappliance 205 may be located on network 104′. In other embodiments, theappliance 205′ may be located on network 104. In some embodiments, theappliance 205′ may be located on network 104′ or network 104″. In oneembodiment, the appliance 205 and 205′ are on the same network. Inanother embodiment, the appliance 205 and 205′ are on differentnetworks. In another example, a first WAN optimization appliance 205 maybe deployed for a first server farm 38 and a second WAN optimizationappliance 205′ for a second server farm 38′

In one embodiment, the appliance 205 is a device for accelerating,optimizing or otherwise improving the performance, operation, or qualityof service of any type and form of network traffic, such as traffic toand/or from a WAN connection. In some embodiments, the appliance 205 isa performance enhancing proxy. In other embodiments, the appliance 205is any type and form of WAN optimization or acceleration device,sometimes also referred to as a WAN optimization controller. In oneembodiment, the appliance 205 is any of the product embodiments referredto as WANScaler manufactured by Citrix Systems, Inc. of Ft. Lauderdale,Fla. In other embodiments, the appliance 205 includes any of the productembodiments referred to as BIG-IP link controller and WANjetmanufactured by F5 Networks, Inc. of Seattle, Wash. In anotherembodiment, the appliance 205 includes any of the WX and WXC WANacceleration device platforms manufactured by Juniper Networks, Inc. ofSunnyvale, Calif. In some embodiments, the appliance 205 includes any ofthe steelhead line of WAN optimization appliances manufactured byRiverbed Technology of San Francisco, Calif. In other embodiments, theappliance 205 includes any of the WAN related devices manufactured byExpand Networks Inc. of Roseland, N.J. In one embodiment, the appliance205 includes any of the WAN related appliances manufactured by PacketeerInc. of Cupertino, Calif., such as the PacketShaper, iShared, and SkyXproduct embodiments provided by Packeteer. In yet another embodiment,the appliance 205 includes any WAN related appliances and/or softwaremanufactured by Cisco Systems, Inc. of San Jose, Calif., such as theCisco Wide Area Network Application Services software and networkmodules, and Wide Area Network engine appliances.

In one embodiment, the appliance 205 provides application and dataacceleration services for branch-office or remote offices. In oneembodiment, the appliance 205 includes optimization of Wide Area FileServices (WAFS). In another embodiment, the appliance 205 acceleratesthe delivery of files, such as via the Common Internet File System(CIFS) protocol. In other embodiments, the appliance 205 providescaching in memory and/or storage to accelerate delivery of applicationsand data. In one embodiment, the appliance 205 provides compression ofnetwork traffic at any level of the network stack or at any protocol ornetwork layer. In another embodiment, the appliance 205 providestransport layer protocol optimizations, flow control, performanceenhancements or modifications and/or management to accelerate deliveryof applications and data over a WAN connection. For example, in oneembodiment, the appliance 205 provides Transport Control Protocol (TCP)optimizations. In other embodiments, the appliance 205 providesoptimizations, flow control, performance enhancements or modificationsand/or management for any session or application layer protocol.

In another embodiment, the appliance 205 encoded any type and form ofdata or information into custom or standard TCP and/or IP header fieldsor option fields of network packet to announce presence, functionalityor capability to another appliance 205′. In another embodiment, anappliance 205′ may communicate with another appliance 205′ using dataencoded in both TCP and/or IP header fields or options. For example, theappliance may use TCP option(s) or IP header fields or options tocommunicate one or more parameters to be used by the appliances 205,205′ in performing functionality, such as WAN acceleration, or forworking in conjunction with each other.

In some embodiments, the appliance 200 preserves any of the informationencoded in TCP and/or IP header and/or option fields communicatedbetween appliances 205 and 205′. For example, the appliance 200 mayterminate a transport layer connection traversing the appliance 200,such as a transport layer connection from between a client and a servertraversing appliances 205 and 205′. In one embodiment, the appliance 200identifies and preserves any encoded information in a transport layerpacket transmitted by a first appliance 205 via a first transport layerconnection and communicates a transport layer packet with the encodedinformation to a second appliance 205′ via a second transport layerconnection.

Referring now to FIG. 1D, a network environment for delivering and/oroperating a computing environment on a client 102 is depicted. In someembodiments, a server 106 includes an application delivery system 190for delivering a computing environment or an application and/or datafile to one or more clients 102. In brief overview, a client 10 is incommunication with a server 106 via network 104, 104′ and appliance 200.For example, the client 102 may reside in a remote office of a company,e.g., a branch office, and the server 106 may reside at a corporate datacenter. The client 102 comprises a client agent 120, and a computingenvironment 15. The computing environment 15 may execute or operate anapplication that accesses, processes or uses a data file. The computingenvironment 15, application and/or data file may be delivered via theappliance 200 and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of acomputing environment 15, or any portion thereof, to a client 102. Inone embodiment, the appliance 200 accelerates the delivery of thecomputing environment 15 by the application delivery system 190. Forexample, the embodiments described herein may be used to acceleratedelivery of a streaming application and data file processable by theapplication from a central corporate data center to a remote userlocation, such as a branch office of the company. In another embodiment,the appliance 200 accelerates transport layer traffic between a client102 and a server 106. The appliance 200 may provide accelerationtechniques for accelerating any transport layer payload from a server106 to a client 102, such as: 1) transport layer connection pooling, 2)transport layer connection multiplexing, 3) transport control protocolbuffering, 4) compression and 5) caching. In some embodiments, theappliance 200 provides load balancing of servers 106 in responding torequests from clients 102. In other embodiments, the appliance 200 actsas a proxy or access server to provide access to the one or more servers106. In another embodiment, the appliance 200 provides a secure virtualprivate network connection from a first network 104 of the client 102 tothe second network 104′ of the server 106, such as an SSL VPNconnection. It yet other embodiments, the appliance 200 providesapplication firewall security, control and management of the connectionand communications between a client 102 and a server 106.

In some embodiments, the application delivery management system 190provides application delivery techniques to deliver a computingenvironment to a desktop of a user, remote or otherwise, based on aplurality of execution methods and based on any authentication andauthorization policies applied via a policy engine 195. With thesetechniques, a remote user may obtain a computing environment and accessto server stored applications and data files from any network connecteddevice 100. In one embodiment, the application delivery system 190 mayreside or execute on a server 106. In another embodiment, theapplication delivery system 190 may reside or execute on a plurality ofservers 106 a-106 n. In some embodiments, the application deliverysystem 190 may execute in a server farm 38. In one embodiment, theserver 106 executing the application delivery system 190 may also storeor provide the application and data file. In another embodiment, a firstset of one or more servers 106 may execute the application deliverysystem 190, and a different server 106 n may store or provide theapplication and data file. In some embodiments, each of the applicationdelivery system 190, the application, and data file may reside or belocated on different servers. In yet another embodiment, any portion ofthe application delivery system 190 may reside, execute or be stored onor distributed to the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 15 for executing anapplication that uses or processes a data file. The client 102 vianetworks 104, 104′ and appliance 200 may request an application and datafile from the server 106. In one embodiment, the appliance 200 mayforward a request from the client 102 to the server 106. For example,the client 102 may not have the application and data file stored oraccessible locally. In response to the request, the application deliverysystem 190 and/or server 106 may deliver the application and data fileto the client 102. For example, in one embodiment, the server 106 maytransmit the application as an application stream to operate incomputing environment 15 on client 102.

In some embodiments, the application delivery system 190 comprises anyportion of the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™ and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application delivery system 190 may deliver one ormore applications to clients 102 or users via a remote-display protocolor otherwise via remote-based or server-based computing. In anotherembodiment, the application delivery system 190 may deliver one or moreapplications to clients or users via steaming of the application.

In one embodiment, the application delivery system 190 includes a policyengine 195 for controlling and managing the access to, selection ofapplication execution methods and the delivery of applications. In someembodiments, the policy engine 195 determines the one or moreapplications a user or client 102 may access. In another embodiment, thepolicy engine 195 determines how the application should be delivered tothe user or client 102, e.g., the method of execution. In someembodiments, the application delivery system 190 provides a plurality ofdelivery techniques from which to select a method of applicationexecution, such as a server-based computing, streaming or delivering theapplication locally to the client 120 for local execution.

In one embodiment, a client 102 requests execution of an applicationprogram and the application delivery system 190 comprising a server 106selects a method of executing the application program. In someembodiments, the server 106 receives credentials from the client 102. Inanother embodiment, the server 106 receives a request for an enumerationof available applications from the client 102. In one embodiment, inresponse to the request or receipt of credentials, the applicationdelivery system 190 enumerates a plurality of application programsavailable to the client 102. The application delivery system 190receives a request to execute an enumerated application. The applicationdelivery system 190 selects one of a predetermined number of methods forexecuting the enumerated application, for example, responsive to apolicy of a policy engine. The application delivery system 190 mayselect a method of execution of the application enabling the client 102to receive application-output data generated by execution of theapplication program on a server 106.

The application delivery system 190 may select a method of execution ofthe application enabling the local machine 10 to execute the applicationprogram locally after retrieving a plurality of application filescomprising the application. In yet another embodiment, the applicationdelivery system 190 may select a method of execution of the applicationto stream the application via the network 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application,which can be any type and/or form of software, program, or executableinstructions such as any type and/or form of web browser, web-basedclient, client-server application, a thin-client computing client, anActiveX control, or a Java applet, or any other type and/or form ofexecutable instructions capable of executing on client 102. In someembodiments, the application may be a server-based or a remote-basedapplication executed on behalf of the client 102 on a server 106. In oneembodiments the server 106 may display output to the client 102 usingany thin-client or remote-display protocol, such as the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash. Theapplication can use any type of protocol and it can be, for example, anHTTP client, an FTP client, an Oscar client, or a Telnet client. Inother embodiments, the application comprises any type of softwarerelated to VoIP communications, such as a soft IP telephone. In furtherembodiments, the application comprises any application related toreal-time data communications, such as applications for streaming videoand/or audio.

In some embodiments, the server 106 or a server farm 38 may be runningone or more applications, such as an application providing a thin-clientcomputing or remote display presentation application. In one embodiment,the server 106 or server farm 38 executes as an application, any portionof the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™, and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application is an ICA client, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla. In other embodiments, theapplication includes a Remote Desktop (RDP) client, developed byMicrosoft Corporation of Redmond, Wash. Also, the server 106 may run anapplication, which for example, may be an application server providingemail services such as Microsoft Exchange manufactured by the MicrosoftCorporation of Redmond, Wash., a web or Internet server, or a desktopsharing server, or a collaboration server. In some embodiments, any ofthe applications may comprise any type of hosted service or products,such as GoToMeeting™ provided by Citrix Online Division, Inc. of SantaBarbara, Calif., WebEx™ provided by WebEx, Inc. of Santa Clara, Calif.,or Microsoft Office Live Meeting provided by Microsoft Corporation ofRedmond, Wash.

Still referring to FIG. 1D, an embodiment of the network environment mayinclude a monitoring server 106A. The monitoring server 106A may includeany type and form performance monitoring service 198. The performancemonitoring service 198 may include monitoring, measurement and/ormanagement software and/or hardware, including data collection,aggregation, analysis, management and reporting. In one embodiment, theperformance monitoring service 198 includes one or more monitoringagents 197. The monitoring agent 197 includes any software, hardware orcombination thereof for performing monitoring, measurement and datacollection activities on a device, such as a client 102, server 106 oran appliance 200, 205. In some embodiments, the monitoring agent 197includes any type and form of script, such as Visual Basic script, orJavascript. In one embodiment, the monitoring agent 197 executestransparently to any application and/or user of the device. In someembodiments, the monitoring agent 197 is installed and operatedunobtrusively to the application or client. In yet another embodiment,the monitoring agent 197 is installed and operated without anyinstrumentation for the application or device.

In some embodiments, the monitoring agent 197 monitors, measures andcollects data on a predetermined frequency. In other embodiments, themonitoring agent 197 monitors, measures and collects data based upondetection of any type and form of event. For example, the monitoringagent 197 may collect data upon detection of a request for a web page orreceipt of an HTTP response. In another example, the monitoring agent197 may collect data upon detection of any user input events, such as amouse click. The monitoring agent 197 may report or provide anymonitored, measured or collected data to the monitoring service 198. Inone embodiment, the monitoring agent 197 transmits information to themonitoring service 198 according to a schedule or a predeterminedfrequency. In another embodiment, the monitoring agent 197 transmitsinformation to the monitoring service 198 upon detection of an event.

In some embodiments, the monitoring service 198 and/or monitoring agent197 performs monitoring and performance measurement of any networkresource or network infrastructure element, such as a client, server,server farm, appliance 200, appliance 205, or network connection. In oneembodiment, the monitoring service 198 and/or monitoring agent 197performs monitoring and performance measurement of any transport layerconnection, such as a TCP or UDP connection. In another embodiment, themonitoring service 198 and/or monitoring agent 197 monitors and measuresnetwork latency. In yet one embodiment, the monitoring service 198and/or monitoring agent 197 monitors and measures bandwidth utilization.

In other embodiments, the monitoring service 198 and/or monitoring agent197 monitors and measures end-user response times. In some embodiments,the monitoring service 198 performs monitoring and performancemeasurement of an application. In another embodiment, the monitoringservice 198 and/or monitoring agent 197 performs monitoring andperformance measurement of any session or connection to the application.In one embodiment, the monitoring service 198 and/or monitoring agent197 monitors and measures performance of a browser. In anotherembodiment, the monitoring service 198 and/or monitoring agent 197monitors and measures performance of HTTP based transactions. In someembodiments, the monitoring service 198 and/or monitoring agent 197monitors and measures performance of a Voice over IP (VoIP) applicationor session. In other embodiments, the monitoring service 198 and/ormonitoring agent 197 monitors and measures performance of a remotedisplay protocol application, such as an ICA client or RDP client. Inyet another embodiment, the monitoring service 198 and/or monitoringagent 197 monitors and measures performance of any type and form ofstreaming media. In still a further embodiment, the monitoring service198 and/or monitoring agent 197 monitors and measures performance of ahosted application or a Software-As-A-Service (SaaS) delivery model.

In some embodiments, the monitoring service 198 and/or monitoring agent197 performs monitoring and performance measurement of one or moretransactions, requests or responses related to application. In otherembodiments, the monitoring service 198 and/or monitoring agent 197monitors and measures any portion of an application layer stack, such asany .NET or J2EE calls. In one embodiment, the monitoring service 198and/or monitoring agent 197 monitors and measures database or SQLtransactions. In yet another embodiment, the monitoring service 198and/or monitoring agent 197 monitors and measures any method, functionor application programming interface (API) call.

In one embodiment, the monitoring service 198 and/or monitoring agent197 performs monitoring and performance measurement of a delivery ofapplication and/or data from a server to a client via one or moreappliances, such as appliance 200 and/or appliance 205. In someembodiments, the monitoring service 198 and/or monitoring agent 197monitors and measures performance of delivery of a virtualizedapplication. In other embodiments, the monitoring service 198 and/ormonitoring agent 197 monitors and measures performance of delivery of astreaming application. In another embodiment, the monitoring service 198and/or monitoring agent 197 monitors and measures performance ofdelivery of a desktop application to a client and/or the execution ofthe desktop application on the client. In another embodiment, themonitoring service 198 and/or monitoring agent 197 monitors and measuresperformance of a client/server application.

In one embodiment, the monitoring service 198 and/or monitoring agent197 is designed and constructed to provide application performancemanagement for the application delivery system 190. For example, themonitoring service 198 and/or monitoring agent 197 may monitor, measureand manage the performance of the delivery of applications via theCitrix Presentation Server. In this example, the monitoring service 198and/or monitoring agent 197 monitors individual ICA sessions. Themonitoring service 198 and/or monitoring agent 197 may measure the totaland per session system resource usage, as well as application andnetworking performance. The monitoring service 198 and/or monitoringagent 197 may identify the active servers for a given user and/or usersession. In some embodiments, the monitoring service 198 and/ormonitoring agent 197 monitors back-end connections between theapplication delivery system 190 and an application and/or databaseserver. The monitoring service 198 and/or monitoring agent 197 maymeasure network latency, delay and volume per user-session or ICAsession.

In some embodiments, the monitoring service 198 and/or monitoring agent197 measures and monitors memory usage for the application deliverysystem 190, such as total memory usage, per user session and/or perprocess. In other embodiments, the monitoring service 198 and/ormonitoring agent 197 measures and monitors CPU usage the applicationdelivery system 190, such as total CPU usage, per user session and/orper process. In another embodiments, the monitoring service 198 and/ormonitoring agent 197 measures and monitors the time required to log-into an application, a server, or the application delivery system, such asCitrix Presentation Server. In one embodiment, the monitoring service198 and/or monitoring agent 197 measures and monitors the duration auser is logged into an application, a server, or the applicationdelivery system 190. In some embodiments, the monitoring service 198and/or monitoring agent 197 measures and monitors active and inactivesession counts for an application, server or application delivery systemsession. In yet another embodiment, the monitoring service 198 and/ormonitoring agent 197 measures and monitors user session latency.

In yet further embodiments, the monitoring service 198 and/or monitoringagent 197 measures and monitors measures and monitors any type and formof server metrics. In one embodiment, the monitoring service 198 and/ormonitoring agent 197 measures and monitors metrics related to systemmemory, CPU usage, and disk storage. In another embodiment, themonitoring service 198 and/or monitoring agent 197 measures and monitorsmetrics related to page faults, such as page faults per second. In otherembodiments, the monitoring service 198 and/or monitoring agent 197measures and monitors round-trip time metrics. In yet anotherembodiment, the monitoring service 198 and/or monitoring agent 197measures and monitors metrics related to application crashes, errorsand/or hangs.

In some embodiments, the monitoring service 198 and monitoring agent 198includes any of the product embodiments referred to as EdgeSightmanufactured by Citrix Systems, Inc. of Ft. Lauderdale, Fla. In anotherembodiment, the performance monitoring service 198 and/or monitoringagent 198 includes any portion of the product embodiments referred to asthe TrueView product suite manufactured by the Symphoniq Corporation ofPalo Alto, Calif. In one embodiment, the performance monitoring service198 and/or monitoring agent 198 includes any portion of the productembodiments referred to as the TeaLeaf CX product suite manufactured bythe TeaLeaf Technology Inc. of San Francisco, Calif. In otherembodiments, the performance monitoring service 198 and/or monitoringagent 198 includes any portion of the business service managementproducts, such as the BMC Performance Manager and Patrol products,manufactured by BMC Software, Inc. of Houston, Tex.

The client 102, server 106, and appliance 200 may be deployed as and/orexecuted on any type and form of computing device, such as a computer,network device or appliance capable of communicating on any type andform of network and performing the operations described herein. FIGS. 1Eand 1F depict block diagrams of a computing device 100 useful forpracticing an embodiment of the client 102, server 106 or appliance 200.As shown in FIGS. 1E and 1F, each computing device 100 includes acentral processing unit 101, and a main memory unit 122. As shown inFIG. 1E, a computing device 100 may include a visual display device 124,a keyboard 126 and/or a pointing device 127, such as a mouse. Eachcomputing device 100 may also include additional optional elements, suchas one or more input/output devices 130 a-130 b (generally referred tousing reference numeral 130), and a cache memory 140 in communicationwith the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds toand processes instructions fetched from the main memory unit 122. Inmany embodiments, the central processing unit is provided by amicroprocessor unit, such as: those manufactured by Intel Corporation ofMountain View, Calif.; those manufactured by Motorola Corporation ofSchaumburg, Ill.; those manufactured by Transmeta Corporation of SantaClara, Calif.; the RS/6000 processor, those manufactured byInternational Business Machines of White Plains, N.Y.; or thosemanufactured by Advanced Micro Devices of Sunnyvale, Calif. Thecomputing device 100 may be based on any of these processors, or anyother processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storingdata and allowing any storage location to be directly accessed by themicroprocessor 101, such as Static random access memory (SRAM), BurstSRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM),Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended DataOutput RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), BurstExtended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM),synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data RateSDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM),Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The mainmemory 122 may be based on any of the above described memory chips, orany other available memory chips capable of operating as describedherein. In the embodiment shown in FIG. 1E, the processor 101communicates with main memory 122 via a system bus 150 (described inmore detail below). FIG. 1E depicts an embodiment of a computing device100 in which the processor communicates directly with main memory 122via a memory port 103. For example, in FIG. 1F the main memory 122 maybe DRDRAM.

FIG. 1F depicts an embodiment in which the main processor 101communicates directly with cache memory 140 via a secondary bus,sometimes referred to as a backside bus. In other embodiments, the mainprocessor 101 communicates with cache memory 140 using the system bus150. Cache memory 140 typically has a faster response time than mainmemory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In theembodiment shown in FIG. 1E, the processor 101 communicates with variousI/O devices 130 via a local system bus 150. Various busses may be usedto connect the central processing unit 101 to any of the I/O devices130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannelArchitecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or aNuBus. For embodiments in which the I/O device is a video display 124,the processor 101 may use an Advanced Graphics Port (AGP) to communicatewith the display 124. FIG. 1F depicts an embodiment of a computer 100 inwhich the main processor 101 communicates directly with I/O device 130via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1F also depicts anembodiment in which local busses and direct communication are mixed: theprocessor 101 communicates with I/O device 130 using a localinterconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device116, such as a floppy disk drive for receiving floppy disks such as3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive,a DVD-ROM drive, tape drives of various formats, USB device, hard-driveor any other device suitable for installing software and programs suchas any client agent 120, or portion thereof. The computing device 100may further comprise a storage device 128, such as one or more hard diskdrives or redundant arrays of independent disks, for storing anoperating system and other related software, and for storing applicationsoftware programs such as any program related to the client agent 120.Optionally, any of the installation devices 116 could also be used asthe storage device 128. Additionally, the operating system and thesoftware can be run from a bootable medium, for example, a bootable CD,such as KNOPPIX®, a bootable CD for GNU/Linux that is available as aGNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface118 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56 kb, X.25), broadband connections (e.g., ISDN, Frame Relay,ATM), wireless connections, or some combination of any or all of theabove. The network interface 118 may comprise a built-in networkadapter, network interface card, PCMCIA network card, card bus networkadapter, wireless network adapter, USB network adapter, modem or anyother device suitable for interfacing the computing device 100 to anytype of network capable of communication and performing the operationsdescribed herein. A wide variety of I/O devices 130 a-130 n may bepresent in the computing device 100. Input devices include keyboards,mice, trackpads, trackballs, microphones, and drawing tablets. Outputdevices include video displays, speakers, inkjet printers, laserprinters, and dye-sublimation printers. The I/O devices 130 may becontrolled by an I/O controller 123 as shown in FIG. 1E. The I/Ocontroller may control one or more I/O devices such as a keyboard 126and a pointing device 127, e.g., a mouse or optical pen. Furthermore, anI/O device may also provide storage 128 and/or an installation medium116 for the computing device 100. In still other embodiments, thecomputing device 100 may provide USB connections to receive handheld USBstorage devices such as the USB Flash Drive line of devices manufacturedby Twintech Industry, Inc. of Los Alamitos, California.

In some embodiments, the computing device 100 may comprise or beconnected to multiple display devices 124 a-124 n, which each may be ofthe same or different type and/or form. As such, any of the I/O devices130 a-130 n and/or the I/O controller 123 may comprise any type and/orform of suitable hardware, software, or combination of hardware andsoftware to support, enable or provide for the connection and use ofmultiple display devices 124 a-124 n by the computing device 100. Forexample, the computing device 100 may include any type and/or form ofvideo adapter, video card, driver, and/or library to interface,communicate, connect or otherwise use the display devices 124 a-124 n.In one embodiment, a video adapter may comprise multiple connectors tointerface to multiple display devices 124 a-124 n. In other embodiments,the computing device 100 may include multiple video adapters, with eachvideo adapter connected to one or more of the display devices 124 a-124n. In some embodiments, any portion of the operating system of thecomputing device 100 may be configured for using multiple displays 124a-124 n. In other embodiments, one or more of the display devices 124a-124 n may be provided by one or more other computing devices, such ascomputing devices 100 a and 100 b connected to the computing device 100,for example, via a network. These embodiments may include any type ofsoftware designed and constructed to use another computer's displaydevice as a second display device 124 a for the computing device 100.One ordinarily skilled in the art will recognize and appreciate thevarious ways and embodiments that a computing device 100 may beconfigured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 betweenthe system bus 150 and an external communication bus, such as a USB bus,an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, aFireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, aGigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, aSuper HIPPI bus, a SerialPlus bus, a SCl/LAMP bus, a FibreChannel bus,or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1E and 1F typicallyoperate under the control of operating systems, which control schedulingof tasks and access to system resources. The computing device 100 can berunning any operating system such as any of the versions of theMicrosoft® Windows operating systems, the different releases of the Unixand Linux operating systems, any version of the Mac OS® for Macintoshcomputers, any embedded operating system, any real-time operatingsystem, any open source operating system, any proprietary operatingsystem, any operating systems for mobile computing devices, or any otheroperating system capable of running on the computing device andperforming the operations described herein. Typical operating systemsinclude: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which aremanufactured by Microsoft Corporation of Redmond, Wash.; MacOS,manufactured by Apple Computer of Cupertino, California; OS/2,manufactured by International Business Machines of Armonk, N.Y.; andLinux, a freely-available operating system distributed by Caldera Corp.of Salt Lake City, Utah, or any type and/or form of a Unix operatingsystem, among others.

In other embodiments, the computing device 100 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment the computer 100 is a Treo 180,270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In thisembodiment, the Treo smart phone is operated under the control of thePalmOS operating system and includes a stylus input device as well as afive-way navigator device. Moreover, the computing device 100 can be anyworkstation, desktop computer, laptop or notebook computer, server,handheld computer, mobile telephone, any other computer, or other formof computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

B. Appliance Architecture

FIG. 2A illustrates an example embodiment of the appliance 200. Thearchitecture of the appliance 200 in FIG. 2A is provided by way ofillustration only and is not intended to be limiting. As shown in FIG.2, appliance 200 comprises a hardware layer 206 and a software layerdivided into a user space 202 and a kernel space 204.

Hardware layer 206 provides the hardware elements upon which programsand services within kernel space 204 and user space 202 are executed.Hardware layer 206 also provides the structures and elements which allowprograms and services within kernel space 204 and user space 202 tocommunicate data both internally and externally with respect toappliance 200. As shown in FIG. 2, the hardware layer 206 includes aprocessing unit 262 for executing software programs and services, amemory 264 for storing software and data, network ports 266 fortransmitting and receiving data over a network, and an encryptionprocessor 260 for performing functions related to Secure Sockets Layerprocessing of data transmitted and received over the network. In someembodiments, the central processing unit 262 may perform the functionsof the encryption processor 260 in a single processor. Additionally, thehardware layer 206 may comprise multiple processors for each of theprocessing unit 262 and the encryption processor 260. The processor 262may include any of the processors 101 described above in connection withFIGS. 1E and 1F. In some embodiments, the central processing unit 262may perform the functions of the encryption processor 260 in a singleprocessor. Additionally, the hardware layer 206 may comprise multipleprocessors for each of the processing unit 262 and the encryptionprocessor 260. For example, in one embodiment, the appliance 200comprises a first processor 262 and a second processor 262′. In otherembodiments, the processor 262 or 262′ comprises a multi-core processor.

Although the hardware layer 206 of appliance 200 is generallyillustrated with an encryption processor 260, processor 260 may be aprocessor for performing functions related to any encryption protocol,such as the Secure Socket Layer (SSL) or Transport Layer Security (TLS)protocol. In some embodiments, the processor 260 may be a generalpurpose processor (GPP), and in further embodiments, may be haveexecutable instructions for performing processing of any securityrelated protocol.

Although the hardware layer 206 of appliance 200 is illustrated withcertain elements in FIG. 2, the hardware portions or components ofappliance 200 may comprise any type and form of elements, hardware orsoftware, of a computing device, such as the computing device 100illustrated and discussed herein in conjunction with FIGS. 1E and 1F. Insome embodiments, the appliance 200 may comprise a server, gateway,router, switch, bridge or other type of computing or network device, andhave any hardware and/or software elements associated therewith.

The operating system of appliance 200 allocates, manages, or otherwisesegregates the available system memory into kernel space 204 and userspace 204. In example software architecture 200, the operating systemmay be any type and/or form of UNIX operating system although theinvention is not so limited. As such, the appliance 200 can be runningany operating system such as any of the versions of the Microsoft®Windows operating systems, the different releases of the Unix and Linuxoperating systems, any version of the Mac OS® for Macintosh computers,any embedded operating system, any network operating system, anyreal-time operating system, any open source operating system, anyproprietary operating system, any operating systems for mobile computingdevices or network devices, or any other operating system capable ofrunning on the appliance 200 and performing the operations describedherein.

The kernel space 204 is reserved for running the kernel 230, includingany device drivers, kernel extensions or other kernel related software.As known to those skilled in the art, the kernel 230 is the core of theoperating system, and provides access, control, and management ofresources and hardware-related elements of the application 104. Inaccordance with an embodiment of the appliance 200, the kernel space 204also includes a number of network services or processes working inconjunction with a cache manager 232, sometimes also referred to as theintegrated cache, the benefits of which are described in detail furtherherein. Additionally, the embodiment of the kernel 230 will depend onthe embodiment of the operating system installed, configured, orotherwise used by the device 200.

In one embodiment, the device 200 comprises one network stack 267, suchas a TCP/IP based stack, for communicating with the client 102 and/orthe server 106. In one embodiment, the network stack 267 is used tocommunicate with a first network, such as network 108, and a secondnetwork 110. In some embodiments, the device 200 terminates a firsttransport layer connection, such as a TCP connection of a client 102,and establishes a second transport layer connection to a server 106 foruse by the client 102, e.g., the second transport layer connection isterminated at the appliance 200 and the server 106. The first and secondtransport layer connections may be established via a single networkstack 267. In other embodiments, the device 200 may comprise multiplenetwork stacks, for example 267 and 267′, and the first transport layerconnection may be established or terminated at one network stack 267,and the second transport layer connection on the second network stack267′. For example, one network stack may be for receiving andtransmitting network packet on a first network, and another networkstack for receiving and transmitting network packets on a secondnetwork. In one embodiment, the network stack 267 comprises a buffer 243for queuing one or more network packets for transmission by theappliance 200.

As shown in FIG. 2, the kernel space 204 includes the cache manager 232,a high-speed layer 2-7 integrated packet engine 240, an encryptionengine 234, a policy engine 236 and multi-protocol compression logic238. Running these components or processes 232, 240, 234, 236 and 238 inkernel space 204 or kernel mode instead of the user space 202 improvesthe performance of each of these components, alone and in combination.Kernel operation means that these components or processes 232, 240, 234,236 and 238 run in the core address space of the operating system of thedevice 200. For example, running the encryption engine 234 in kernelmode improves encryption performance by moving encryption and decryptionoperations to the kernel, thereby reducing the number of transitionsbetween the memory space or a kernel thread in kernel mode and thememory space or a thread in user mode. For example, data obtained inkernel mode may not need to be passed or copied to a process or threadrunning in user mode, such as from a kernel level data structure to auser level data structure. In another aspect, the number of contextswitches between kernel mode and user mode are also reduced.Additionally, synchronization of and communications between any of thecomponents or processes 232, 240, 235, 236 and 238 can be performed moreefficiently in the kernel space 204.

In some embodiments, any portion of the components 232, 240, 234, 236and 238 may run or operate in the kernel space 204, while other portionsof these components 232, 240, 234, 236 and 238 may run or operate inuser space 202. In one embodiment, the appliance 200 uses a kernel-leveldata structure providing access to any portion of one or more networkpackets, for example, a network packet comprising a request from aclient 102 or a response from a server 106. In some embodiments, thekernel-level data structure may be obtained by the packet engine 240 viaa transport layer driver interface or filter to the network stack 267.The kernel-level data structure may comprise any interface and/or dataaccessible via the kernel space 204 related to the network stack 267,network traffic or packets received or transmitted by the network stack267. In other embodiments, the kernel-level data structure may be usedby any of the components or processes 232, 240, 234, 236 and 238 toperform the desired operation of the component or process. In oneembodiment, a component 232, 240, 234, 236 and 238 is running in kernelmode 204 when using the kernel-level data structure, while in anotherembodiment, the component 232, 240, 234, 236 and 238 is running in usermode when using the kernel-level data structure. In some embodiments,the kernel-level data structure may be copied or passed to a secondkernel-level data structure, or any desired user-level data structure.

The cache manager 232 may comprise software, hardware or any combinationof software and hardware to provide cache access, control and managementof any type and form of content, such as objects or dynamicallygenerated objects served by the originating servers 106. The data,objects or content processed and stored by the cache manager 232 maycomprise data in any format, such as a markup language, or communicatedvia any protocol. In some embodiments, the cache manager 232 duplicatesoriginal data stored elsewhere or data previously computed, generated ortransmitted, in which the original data may require longer access timeto fetch, compute or otherwise obtain relative to reading a cache memoryelement. Once the data is stored in the cache memory element, future usecan be made by accessing the cached copy rather than refetching orrecomputing the original data, thereby reducing the access time. In someembodiments, the cache memory element may comprise a data object inmemory 264 of device 200. In other embodiments, the cache memory elementmay comprise memory having a faster access time than memory 264. Inanother embodiment, the cache memory element may comprise any type andform of storage element of the device 200, such as a portion of a harddisk. In some embodiments, the processing unit 262 may provide cachememory for use by the cache manager 232. In yet further embodiments, thecache manager 232 may use any portion and combination of memory,storage, or the processing unit for caching data, objects, and othercontent.

Furthermore, the cache manager 232 includes any logic, functions, rules,or operations to perform any embodiments of the techniques of theappliance 200 described herein. For example, the cache manager 232includes logic or functionality to invalidate objects based on theexpiration of an invalidation time period or upon receipt of aninvalidation command from a client 102 or server 106. In someembodiments, the cache manager 232 may operate as a program, service,process or task executing in the kernel space 204, and in otherembodiments, in the user space 202. In one embodiment, a first portionof the cache manager 232 executes in the user space 202 while a secondportion executes in the kernel space 204. In some embodiments, the cachemanager 232 can comprise any type of general purpose processor (GPP), orany other type of integrated circuit, such as a Field Programmable GateArray (FPGA), Programmable Logic Device (PLD), or Application SpecificIntegrated Circuit (ASIC).

The policy engine 236 may include, for example, an intelligentstatistical engine or other programmable application(s). In oneembodiment, the policy engine 236 provides a configuration mechanism toallow a user to identify, specify, define or configure a caching policy.Policy engine 236, in some embodiments, also has access to memory tosupport data structures such as lookup tables or hash tables to enableuser-selected caching policy decisions. In other embodiments, the policyengine 236 may comprise any logic, rules, functions or operations todetermine and provide access, control and management of objects, data orcontent being cached by the appliance 200 in addition to access, controland management of security, network traffic, network access, compressionor any other function or operation performed by the appliance 200.Further examples of specific caching policies are further describedherein.

In some embodiments, the policy engine 236 may provide a configurationmechanism to allow a user to identify, specify, define or configurepolicies directing behavior of any other components or functionality ofan appliance, including without limitation the components described inFIG. 2B such as vServers 275, VPN functions 280, Intranet IP functions282, switching functions 284, DNS functions 286, acceleration functions288, application firewall functions 290, and monitoring agents 197. Inother embodiments, the policy engine 236 may check, evaluate, implement,or otherwise act in response to any configured policies, and may alsodirect the operation of one or more appliance functions in response to apolicy.

The encryption engine 234 comprises any logic, business rules, functionsor operations for handling the processing of any security relatedprotocol, such as SSL or TLS, or any function related thereto. Forexample, the encryption engine 234 encrypts and decrypts networkpackets, or any portion thereof, communicated via the appliance 200. Theencryption engine 234 may also setup or establish SSL or TLS connectionson behalf of the client 102 a-102 n, server 106 a-106 n, or appliance200. As such, the encryption engine 234 provides offloading andacceleration of SSL processing. In one embodiment, the encryption engine234 uses a tunneling protocol to provide a virtual private networkbetween a client 102 a-102 n and a server 106 a-106 n. In someembodiments, the encryption engine 234 is in communication with theEncryption processor 260. In other embodiments, the encryption engine234 comprises executable instructions running on the Encryptionprocessor 260.

The multi-protocol compression engine 238 comprises any logic, businessrules, function or operations for compressing one or more protocols of anetwork packet, such as any of the protocols used by the network stack267 of the device 200. In one embodiment, multi-protocol compressionengine 238 compresses bi-directionally between clients 102 a-102 n andservers 106 a-106 n any TCP/IP based protocol, including MessagingApplication Programming Interface (MAPI) (email), File Transfer Protocol(FTP), HyperText Transfer Protocol (HTTP), Common Internet File System(CIFS) protocol (file transfer), Independent Computing Architecture(ICA) protocol, Remote Desktop Protocol (RDP), Wireless ApplicationProtocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol.In other embodiments, multi-protocol compression engine 238 providescompression of Hypertext Markup Language (HTML) based protocols and insome embodiments, provides compression of any markup languages, such asthe Extensible Markup Language (XML). In one embodiment, themulti-protocol compression engine 238 provides compression of anyhigh-performance protocol, such as any protocol designed for appliance200 to appliance 200 communications. In another embodiment, themulti-protocol compression engine 238 compresses any payload of or anycommunication using a modified transport control protocol, such asTransaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK),TCP with large windows (TCP-LW), a congestion prediction protocol suchas the TCP-Vegas protocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 acceleratesperformance for users accessing applications via desktop clients, e.g.,Microsoft Outlook and non-Web thin clients, such as any client launchedby popular enterprise applications like Oracle, SAP and Siebel, and evenmobile clients, such as the Pocket PC. In some embodiments, themulti-protocol compression engine 238 by executing in the kernel mode204 and integrating with packet processing engine 240 accessing thenetwork stack 267 is able to compress any of the protocols carried bythe TCP/IP protocol, such as any application layer protocol.

High speed layer 2-7 integrated packet engine 240, also generallyreferred to as a packet processing engine or packet engine, isresponsible for managing the kernel-level processing of packets receivedand transmitted by appliance 200 via network ports 266. The high speedlayer 2-7 integrated packet engine 240 may comprise a buffer for queuingone or more network packets during processing, such as for receipt of anetwork packet or transmission of a network packer. Additionally, thehigh speed layer 2-7 integrated packet engine 240 is in communicationwith one or more network stacks 267 to send and receive network packetsvia network ports 266. The high speed layer 2-7 integrated packet engine240 works in conjunction with encryption engine 234, cache manager 232,policy engine 236 and multi-protocol compression logic 238. Inparticular, encryption engine 234 is configured to perform SSLprocessing of packets, policy engine 236 is configured to performfunctions related to traffic management such as request-level contentswitching and request-level cache redirection, and multi-protocolcompression logic 238 is configured to perform functions related tocompression and decompression of data.

The high speed layer 2-7 integrated packet engine 240 includes a packetprocessing timer 242. In one embodiment, the packet processing timer 242provides one or more time intervals to trigger the processing ofincoming, i.e., received, or outgoing, i.e., transmitted, networkpackets. In some embodiments, the high speed layer 2-7 integrated packetengine 240 processes network packets responsive to the timer 242. Thepacket processing timer 242 provides any type and form of signal to thepacket engine 240 to notify, trigger, or communicate a time relatedevent, interval or occurrence. In many embodiments, the packetprocessing timer 242 operates in the order of milliseconds, such as forexample 100 ms, 50 ms or 25 ms. For example, in some embodiments, thepacket processing timer 242 provides time intervals or otherwise causesa network packet to be processed by the high speed layer 2-7 integratedpacket engine 240 at a 10 ms time interval, while in other embodiments,at a 5 ms time interval, and still yet in further embodiments, as shortas a 3, 2, or 1 ms time interval.

The high speed layer 2-7 integrated packet engine 240 may be interfaced,integrated or in communication with the encryption engine 234, cachemanager 232, policy engine 236 and multi-protocol compression engine 238during operation. As such, any of the logic, functions, or operations ofthe encryption engine 234, cache manager 232, policy engine 236 andmulti-protocol compression logic 238 may be performed responsive to thepacket processing timer 242 and/or the packet engine 240. Therefore, anyof the logic, functions, or operations of the encryption engine 234,cache manager 232, policy engine 236 and multi-protocol compressionlogic 238 may be performed at the granularity of time intervals providedvia the packet processing timer 242, for example, at a time interval ofless than or equal to 10 ms. For example, in one embodiment, the cachemanager 232 may perform invalidation of any cached objects responsive tothe high speed layer 2-7 integrated packet engine 240 and/or the packetprocessing timer 242. In another embodiment, the expiry or invalidationtime of a cached object can be set to the same order of granularity asthe time interval of the packet processing timer 242, such as at every10 ms.

In contrast to kernel space 204, user space 202 is the memory area orportion of the operating system used by user mode applications orprograms otherwise running in user mode. A user mode application may notaccess kernel space 204 directly and uses service calls in order toaccess kernel services. As shown in FIG. 2, user space 202 of appliance200 includes a graphical user interface (GUI) 210, a command lineinterface (CLI) 212, shell services 214, health monitoring program 216,and daemon services 218. GUI 210 and CLI 212 provide a means by which asystem administrator or other user can interact with and control theoperation of appliance 200, such as via the operating system of theappliance 200 and either is user space 202 or kernel space 204. The GUI210 may be any type and form of graphical user interface and may bepresented via text, graphical or otherwise, by any type of program orapplication, such as a browser. The CLI 212 may be any type and form ofcommand line or text-based interface, such as a command line provided bythe operating system. For example, the CLI 212 may comprise a shell,which is a tool to enable users to interact with the operating system.In some embodiments, the CLI 212 may be provided via a bash, csh, tcsh,or ksh type shell. The shell services 214 comprises the programs,services, tasks, processes or executable instructions to supportinteraction with the appliance 200 or operating system by a user via theGUI 210 and/or CLI 212.

Health monitoring program 216 is used to monitor, check, report andensure that network systems are functioning properly and that users arereceiving requested content over a network. Health monitoring program216 comprises one or more programs, services, tasks, processes orexecutable instructions to provide logic, rules, functions or operationsfor monitoring any activity of the appliance 200. In some embodiments,the health monitoring program 216 intercepts and inspects any networktraffic passed via the appliance 200. In other embodiments, the healthmonitoring program 216 interfaces by any suitable means and/ormechanisms with one or more of the following: the encryption engine 234,cache manager 232, policy engine 236, multi-protocol compression logic238, packet engine 240, daemon services 218, and shell services 214. Assuch, the health monitoring program 216 may call any applicationprogramming interface (API) to determine a state, status, or health ofany portion of the appliance 200. For example, the health monitoringprogram 216 may ping or send a status inquiry on a periodic basis tocheck if a program, process, service or task is active and currentlyrunning. In another example, the health monitoring program 216 may checkany status, error or history logs provided by any program, process,service or task to determine any condition, status or error with anyportion of the appliance 200.

Daemon services 218 are programs that run continuously or in thebackground and handle periodic service requests received by appliance200. In some embodiments, a daemon service may forward the requests toother programs or processes, such as another daemon service 218 asappropriate. As known to those skilled in the art, a daemon service 218may run unattended to perform continuous or periodic system widefunctions, such as network control, or to perform any desired task. Insome embodiments, one or more daemon services 218 run in the user space202, while in other embodiments, one or more daemon services 218 run inthe kernel space.

Referring now to FIG. 2B, another embodiment of the appliance 200 isdepicted. In brief overview, the appliance 200 provides one or more ofthe following services, functionality or operations: SSL VPNconnectivity 280, switching/load balancing 284, Domain Name Serviceresolution 286, acceleration 288 and an application firewall 290 forcommunications between one or more clients 102 and one or more servers106. Each of the servers 106 may provide one or more network relatedservices 270 a-270 n (referred to as services 270). For example, aserver 106 may provide an http service 270. The appliance 200 comprisesone or more virtual servers or virtual internet protocol servers,referred to as a vServer, VIP server, or just VIP 275 a-275 n (alsoreferred herein as vServer 275). The vServer 275 receives, intercepts orotherwise processes communications between a client 102 and a server 106in accordance with the configuration and operations of the appliance200.

The vServer 275 may comprise software, hardware or any combination ofsoftware and hardware. The vServer 275 may comprise any type and form ofprogram, service, task, process or executable instructions operating inuser mode 202, kernel mode 204 or any combination thereof in theappliance 200. The vServer 275 includes any logic, functions, rules, oroperations to perform any embodiments of the techniques describedherein, such as SSL VPN 280, switching/load balancing 284, Domain NameService resolution 286, acceleration 288 and an application firewall290. In some embodiments, the vServer 275 establishes a connection to aservice 270 of a server 106. The service 275 may comprise any program,application, process, task or set of executable instructions capable ofconnecting to and communicating to the appliance 200, client 102 orvServer 275. For example, the service 275 may comprise a web server,http server, ftp, email or database server. In some embodiments, theservice 270 is a daemon process or network driver for listening,receiving and/or sending communications for an application, such asemail, database or an enterprise application. In some embodiments, theservice 270 may communicate on a specific IP address, or IP address andport.

In some embodiments, the vServer 275 applies one or more policies of thepolicy engine 236 to network communications between the client 102 andserver 106. In one embodiment, the policies are associated with aVServer 275. In another embodiment, the policies are based on a user, ora group of users. In yet another embodiment, a policy is global andapplies to one or more vServers 275 a-275 n, and any user or group ofusers communicating via the appliance 200. In some embodiments, thepolicies of the policy engine have conditions upon which the policy isapplied based on any content of the communication, such as internetprotocol address, port, protocol type, header or fields in a packet, orthe context of the communication, such as user, group of the user,vServer 275, transport layer connection, and/or identification orattributes of the client 102 or server 106.

In other embodiments, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to access the computingenvironment 15, application, and/or data file from a server 106. Inanother embodiment, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to have the application deliverysystem 190 deliver one or more of the computing environment 15,application, and/or data file. In yet another embodiment, the appliance200 establishes a VPN or SSL VPN connection based on the policy engine's236 authentication and/or authorization of a remote user or a remoteclient 103 In one embodiment, the appliance 102 controls the flow ofnetwork traffic and communication sessions based on policies of thepolicy engine 236. For example, the appliance 200 may control the accessto a computing environment 15, application or data file based on thepolicy engine 236.

In some embodiments, the vServer 275 establishes a transport layerconnection, such as a TCP or UDP connection with a client 102 via theclient agent 120. In one embodiment, the vServer 275 listens for andreceives communications from the client 102. In other embodiments, thevServer 275 establishes a transport layer connection, such as a TCP orUDP connection with a client server 106. In one embodiment, the vServer275 establishes the transport layer connection to an internet protocoladdress and port of a server 270 running on the server 106. In anotherembodiment, the vServer 275 associates a first transport layerconnection to a client 102 with a second transport layer connection tothe server 106. In some embodiments, a vServer 275 establishes a pool oftransport layer connections to a server 106 and multiplexes clientrequests via the pooled transport layer connections.

In some embodiments, the appliance 200 provides a SSL VPN connection 280between a client 102 and a server 106. For example, a client 102 on afirst network 102 requests to establish a connection to a server 106 ona second network 104′. In some embodiments, the second network 104′ isnot routable from the first network 104. In other embodiments, theclient 102 is on a public network 104 and the server 106 is on a privatenetwork 104′, such as a corporate network. In one embodiment, the clientagent 120 intercepts communications of the client 102 on the firstnetwork 104, encrypts the communications, and transmits thecommunications via a first transport layer connection to the appliance200. The appliance 200 associates the first transport layer connectionon the first network 104 to a second transport layer connection to theserver 106 on the second network 104. The appliance 200 receives theintercepted communication from the client agent 102, decrypts thecommunications, and transmits the communication to the server 106 on thesecond network 104 via the second transport layer connection. The secondtransport layer connection may be a pooled transport layer connection.As such, the appliance 200 provides an end-to-end secure transport layerconnection for the client 102 between the two networks 104, 104′.

In one embodiment, the appliance 200 hosts an intranet internet protocolor intranetIP 282 address of the client 102 on the virtual privatenetwork 104. The client 102 has a local network identifier, such as aninternet protocol (IP) address and/or host name on the first network104. When connected to the second network 104′ via the appliance 200,the appliance 200 establishes, assigns or otherwise provides anIntranetIP, which is network identifier, such as IP address and/or hostname, for the client 102 on the second network 104′. The appliance 200listens for and receives on the second or private network 104′ for anycommunications directed towards the client 102 using the client'sestablished IntranetIP 282. In one embodiment, the appliance 200 acts asor on behalf of the client 102 on the second private network 104. Forexample, in another embodiment, a vServer 275 listens for and respondsto communications to the IntranetIP 282 of the client 102. In someembodiments, if a computing device 100 on the second network 104′transmits a request, the appliance 200 processes the request as if itwere the client 102. For example, the appliance 200 may respond to aping to the client's IntranetIP 282. In another example, the appliancemay establish a connection, such as a TCP or UDP connection, withcomputing device 100 on the second network 104 requesting a connectionwith the client's IntranetIP 282.

In some embodiments, the appliance 200 provides one or more of thefollowing acceleration techniques 288 to communications between theclient 102 and server 106: 1) compression; 2) decompression; 3)Transmission Control Protocol pooling; 4) Transmission Control Protocolmultiplexing; 5) Transmission Control Protocol buffering; and 6)caching. In one embodiment, the appliance 200 relieves servers 106 ofmuch of the processing load caused by repeatedly opening and closingtransport layers connections to clients 102 by opening one or moretransport layer connections with each server 106 and maintaining theseconnections to allow repeated data accesses by clients via the Internet.This technique is referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from aclient 102 to a server 106 via a pooled transport layer connection, theappliance 200 translates or multiplexes communications by modifyingsequence number and acknowledgment numbers at the transport layerprotocol level. This is referred to as “connection multiplexing”. Insome embodiments, no application layer protocol interaction is required.For example, in the case of an in-bound packet (that is, a packetreceived from a client 102), the source network address of the packet ischanged to that of an output port of appliance 200, and the destinationnetwork address is changed to that of the intended server. In the caseof an outbound packet (that is, one received from a server 106), thesource network address is changed from that of the server 106 to that ofan output port of appliance 200 and the destination address is changedfrom that of appliance 200 to that of the requesting client 102. Thesequence numbers and acknowledgment numbers of the packet are alsotranslated to sequence numbers and acknowledgement expected by theclient 102 on the appliance's 200 transport layer connection to theclient 102. In some embodiments, the packet checksum of the transportlayer protocol is recalculated to account for these translations.

In another embodiment, the appliance 200 provides switching orload-balancing functionality 284 for communications between the client102 and server 106. In some embodiments, the appliance 200 distributestraffic and directs client requests to a server 106 based on layer 4 orapplication-layer request data. In one embodiment, although the networklayer or layer 2 of the network packet identifies a destination server106, the appliance 200 determines the server 106 to distribute thenetwork packet by application information and data carried as payload ofthe transport layer packet. In one embodiment, the health monitoringprograms 216 of the appliance 200 monitor the health of servers todetermine the server 106 for which to distribute a client's request. Insome embodiments, if the appliance 200 detects a server 106 is notavailable or has a load over a predetermined threshold, the appliance200 can direct or distribute client requests to another server 106.

In some embodiments, the appliance 200 acts as a Domain Name Service(DNS) resolver or otherwise provides resolution of a DNS request fromclients 102. In some embodiments, the appliance intercepts' a DNSrequest transmitted by the client 102. In one embodiment, the appliance200 responds to a client's DNS request with an IP address of or hostedby the appliance 200. In this embodiment, the client 102 transmitsnetwork communication for the domain name to the appliance 200. Inanother embodiment, the appliance 200 responds to a client's DNS requestwith an IP address of or hosted by a second appliance 200′. In someembodiments, the appliance 200 responds to a client's DNS request withan IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 200 provides applicationfirewall functionality 290 for communications between the client 102 andserver 106. In one embodiment, the policy engine 236 provides rules fordetecting and blocking illegitimate requests. In some embodiments, theapplication firewall 290 protects against denial of service (DoS)attacks. In other embodiments, the appliance inspects the content ofintercepted requests to identify and block application-based attacks. Insome embodiments, the rules/policy engine 236 comprises one or moreapplication firewall or security control policies for providingprotections against various classes and types of web or Internet basedvulnerabilities, such as one or more of the following: 1) bufferoverflow, 2) CGI-BIN parameter manipulation, 3) form/hidden fieldmanipulation, 4) forceful browsing, 5) cookie or session poisoning, 6)broken access control list (ACLs) or weak passwords, 7) cross-sitescripting (XSS), 8) command injection, 9) SQL injection, 10) errortriggering sensitive information leak, 11) insecure use of cryptography,12) server misconfiguration, 13) back doors and debug options, 14)website defacement, 15) platform or operating systems vulnerabilities,and 16) zero-day exploits. In an embodiment, the application firewall290 provides HTML form field protection in the form of inspecting oranalyzing the network communication for one or more of the following: 1)required fields are returned, 2) no added field allowed, 3) read-onlyand hidden field enforcement, 4) drop-down list and radio button fieldconformance, and 5) form-field max-length enforcement. In someembodiments, the application firewall 290 ensures cookies are notmodified. In other embodiments, the application firewall 290 protectsagainst forceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall 290 protectsany confidential information contained in the network communication. Theapplication firewall 290 may inspect or analyze any networkcommunication in accordance with the rules or polices of the engine 236to identify any confidential information in any field of the networkpacket. In some embodiments, the application firewall 290 identifies inthe network communication one or more occurrences of a credit cardnumber, password, social security number, name, patient code, contactinformation, and age. The encoded portion of the network communicationmay comprise these occurrences or the confidential information. Based onthese occurrences, in one embodiment, the application firewall 290 maytake a policy action on the network communication, such as preventtransmission of the network communication. In another embodiment, theapplication firewall 290 may rewrite, remove or otherwise mask suchidentified occurrence or confidential information.

Still referring to FIG. 2B, the appliance 200 may include a performancemonitoring agent 197 as discussed above in conjunction with FIG. 1D. Inone embodiment, the appliance 200 receives the monitoring agent 197 fromthe monitoring service 1908 or monitoring server 106 as depicted in FIG.1D. In some embodiments, the appliance 200 stores the monitoring agent197 in storage, such as disk, for delivery to any client or server incommunication with the appliance 200. For example, in one embodiment,the appliance 200 transmits the monitoring agent 197 to a client uponreceiving a request to establish a transport layer connection. In otherembodiments, the appliance 200 transmits the monitoring agent 197 uponestablishing the transport layer connection with the client 102. Inanother embodiment, the appliance 200 transmits the monitoring agent 197to the client upon intercepting or detecting a request for a web page.In yet another embodiment, the appliance 200 transmits the monitoringagent 197 to a client or a server in response to a request from themonitoring server 198. In one embodiment, the appliance 200 transmitsthe monitoring agent 197 to a second appliance 200′ or appliance 205.

In other embodiments, the appliance 200 executes the monitoring agent197. In one embodiment, the monitoring agent 197 measures and monitorsthe performance of any application, program, process, service, task orthread executing on the appliance 200. For example, the monitoring agent197 may monitor and measure performance and operation of vServers275A-275N. In another embodiment, the monitoring agent 197 measures andmonitors the performance of any transport layer connections of theappliance 200. In some embodiments, the monitoring agent 197 measuresand monitors the performance of any user sessions traversing theappliance 200. In one embodiment, the monitoring agent 197 measures andmonitors the performance of any virtual private network connectionsand/or sessions traversing the appliance 200, such an SSL VPN session.In still further embodiments, the monitoring agent 197 measures andmonitors the memory, CPU and disk usage and performance of the appliance200. In yet another embodiment, the monitoring agent 197 measures andmonitors the performance of any acceleration technique 288 performed bythe appliance 200, such as SSL offloading, connection pooling andmultiplexing, caching, and compression. In some embodiments, themonitoring agent 197 measures and monitors the performance of any loadbalancing and/or content switching 284 performed by the appliance 200.In other embodiments, the monitoring agent 197 measures and monitors theperformance of application firewall 290 protection and processingperformed by the appliance 200.

C. Client Agent

Referring now to FIG. 3, an embodiment of the client agent 120 isdepicted. The client 102 includes a client agent 120 for establishingand exchanging communications with the appliance 200 and/or server 106via a network 104. In brief overview, the client 102 operates oncomputing device 100 having an operating system with a kernel mode 302and a user mode 303, and a network stack 310 with one or more layers 310a-310 b. The client 102 may have installed and/or execute one or moreapplications. In some embodiments, one or more applications maycommunicate via the network stack 310 to a network 104. One of theapplications, such as a web browser, may also include a first program322. For example, the first program 322 may be used in some embodimentsto install and/or execute the client agent 120, or any portion thereof.The client agent 120 includes an interception mechanism, or interceptor350, for intercepting network communications from the network stack 310from the one or more applications.

The network stack 310 of the client 102 may comprise any type and formof software, or hardware, or any combinations thereof, for providingconnectivity to and communications with a network. In one embodiment,the network stack 310 comprises a software implementation for a networkprotocol suite. The network stack 310 may comprise one or more networklayers, such as any networks layers of the Open Systems Interconnection(OSI) communications model as those skilled in the art recognize andappreciate. As such, the network stack 310 may comprise any type andform of protocols for any of the following layers of the OSI model: 1)physical link layer, 2) data link layer, 3) network layer, 4) transportlayer, 5) session layer, 6) presentation layer, and 7) applicationlayer. In one embodiment, the network stack 310 may comprise a transportcontrol protocol (TCP) over the network layer protocol of the internetprotocol (IP), generally referred to as TCP/IP. In some embodiments, theTCP/IP protocol may be carried over the Ethernet protocol, which maycomprise any of the family of IEEE wide-area-network (WAN) orlocal-area-network (LAN) protocols, such as those protocols covered bythe IEEE 802.3. In some embodiments, the network stack 310 comprises anytype and form of a wireless protocol, such as IEEE 802.11 and/or mobileinternet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may beused, including Messaging Application Programming Interface (MAPI)(email), File Transfer Protocol (FTP), HyperText Transfer Protocol(HTTP), Common Internet File System (CIFS) protocol (file transfer),Independent Computing Architecture (ICA) protocol, Remote DesktopProtocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol,and Voice Over IP (VoIP) protocol. In another embodiment, the networkstack 310 comprises any type and form of transport control protocol,such as a modified transport control protocol, for example a TransactionTCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP withlarge windows (TCP-LW), a congestion prediction protocol such as theTCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments,any type and form of user datagram protocol (UDP), such as UDP over IP,may be used by the network stack 310, such as for voice communicationsor real-time data communications.

Furthermore, the network stack 310 may include one or more networkdrivers supporting the one or more layers, such as a TCP driver or anetwork layer driver. The network drivers may be included as part of theoperating system of the computing device 100 or as part of any networkinterface cards or other network access components of the computingdevice 100. In some embodiments, any of the network drivers of thenetwork stack 310 may be customized, modified or adapted to provide acustom or modified portion of the network stack 310 in support of any ofthe techniques described herein. In other embodiments, the accelerationprogram 120 is designed and constructed to operate with or work inconjunction with the network stack 310 installed or otherwise providedby the operating system of the client 102.

The network stack 310 comprises any type and form of interfaces forreceiving, obtaining, providing or otherwise accessing any informationand data related to network communications of the client 102. In oneembodiment, an interface to the network stack 310 comprises anapplication programming interface (API). The interface may also compriseany function call, hooking or filtering mechanism, event or call backmechanism, or any type of interfacing technique. The network stack 310via the interface may receive or provide any type and form of datastructure, such as an object, related to functionality or operation ofthe network stack 310. For example, the data structure may compriseinformation and data related to a network packet or one or more networkpackets. In some embodiments, the data structure comprises a portion ofthe network packet processed at a protocol layer of the network stack310, such as a network packet of the transport layer. In someembodiments, the data structure 325 comprises a kernel-level datastructure, while in other embodiments, the data structure 325 comprisesa user-mode data structure. A kernel-level data structure may comprise adata structure obtained or related to a portion of the network stack 310operating in kernel-mode 302, or a network driver or other softwarerunning in kernel-mode 302, or any data structure obtained or receivedby a service, process, task, thread or other executable instructionsrunning or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 310 may execute oroperate in kernel-mode 302, for example, the data link or network layer,while other portions execute or operate in user-mode 303, such as anapplication layer of the network stack 310. For example, a first portion310 a of the network stack may provide user-mode access to the networkstack 310 to an application while a second portion 310 a of the networkstack 310 provides access to a network. In some embodiments, a firstportion 310 a of the network stack may comprise one or more upper layersof the network stack 310, such as any of layers 5-7. In otherembodiments, a second portion 310 b of the network stack 310 comprisesone or more lower layers, such as any of layers 1-4. Each of the firstportion 310 a and second portion 310 b of the network stack 310 maycomprise any portion of the network stack 310, at any one or morenetwork layers, in user-mode 203, kernel-mode, 202, or combinationsthereof, or at any portion of a network layer or interface point to anetwork layer or any portion of or interface point to the user-mode 203and kernel-mode 203.

The interceptor 350 may comprise software, hardware, or any combinationof software and hardware. In one embodiment, the interceptor 350intercept a network communication at any point in the network stack 310,and redirects or transmits the network communication to a destinationdesired, managed or controlled by the interceptor 350 or client agent120. For example, the interceptor 350 may intercept a networkcommunication of a network stack 310 of a first network and transmit thenetwork communication to the appliance 200 for transmission on a secondnetwork 104. In some embodiments, the interceptor 350 comprises any typeinterceptor 350 comprises a driver, such as a network driver constructedand designed to interface and work with the network stack 310. In someembodiments, the client agent 120 and/or interceptor 350 operates at oneor more layers of the network stack 310, such as at the transport layer.In one embodiment, the interceptor 350 comprises a filter driver,hooking mechanism, or any form and type of suitable network driverinterface that interfaces to the transport layer of the network stack,such as via the transport driver interface (TDI). In some embodiments,the interceptor 350 interfaces to a first protocol layer, such as thetransport layer and another protocol layer, such as any layer above thetransport protocol layer, for example, an application protocol layer. Inone embodiment, the interceptor 350 may comprise a driver complying withthe Network Driver Interface Specification (NDIS), or a NDIS driver. Inanother embodiment, the interceptor 350 may comprise a min-filter or amini-port driver. In one embodiment, the interceptor 350, or portionthereof, operates in kernel-mode 202. In another embodiment, theinterceptor 350, or portion thereof, operates in user-mode 203. In someembodiments, a portion of the interceptor 350 operates in kernel-mode202 while another portion of the interceptor 350 operates in user-mode203. In other embodiments, the client agent 120 operates in user-mode203 but interfaces via the interceptor 350 to a kernel-mode driver,process, service, task or portion of the operating system, such as toobtain a kernel-level data structure 225. In further embodiments, theinterceptor 350 is a user-mode application or program, such asapplication.

In one embodiment, the interceptor 350 intercepts any transport layerconnection requests. In these embodiments, the interceptor 350 executetransport layer application programming interface (API) calls to set thedestination information, such as destination IP address and/or port to adesired location for the location. In this manner, the interceptor 350intercepts and redirects the transport layer connection to a IP addressand port controlled or managed by the interceptor 350 or client agent120. In one embodiment, the interceptor 350 sets the destinationinformation for the connection to a local IP address and port of theclient 102 on which the client agent 120 is listening. For example, theclient agent 120 may comprise a proxy service listening on a local IPaddress and port for redirected transport layer communications. In someembodiments, the client agent 120 then communicates the redirectedtransport layer communication to the appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain NameService (DNS) request. In one embodiment, the client agent 120 and/orinterceptor 350 resolves the DNS request. In another embodiment, theinterceptor transmits the intercepted DNS request to the appliance 200for DNS resolution. In one embodiment, the appliance 200 resolves theDNS request and communicates the DNS response to the client agent 120.In some embodiments, the appliance 200 resolves the DNS request viaanother appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may comprise two agents120 and 120′. In one embodiment, a first agent 120 may comprise aninterceptor 350 operating at the network layer of the network stack 310.In some embodiments, the first agent 120 intercepts network layerrequests such as Internet Control Message Protocol (ICMP) requests(e.g., ping and traceroute). In other embodiments, the second agent 120′may operate at the transport layer and intercept transport layercommunications. In some embodiments, the first agent 120 interceptscommunications at one layer of the network stack 210 and interfaces withor communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interfacewith a protocol layer in a manner transparent to any other protocollayer of the network stack 310. For example, in one embodiment, theinterceptor 350 operates or interfaces with the transport layer of thenetwork stack 310 transparently to any protocol layer below thetransport layer, such as the network layer, and any protocol layer abovethe transport layer, such as the session, presentation or applicationlayer protocols. This allows the other protocol layers of the networkstack 310 to operate as desired and without modification for using theinterceptor 350. As such, the client agent 120 and/or interceptor 350can interface with the transport layer to secure, optimize, accelerate,route or load-balance any communications provided via any protocolcarried by the transport layer, such as any application layer protocolover TCP/IP.

Furthermore, the client agent 120 and/or interceptor may operate at orinterface with the network stack 310 in a manner transparent to anyapplication, a user of the client 102, and any other computing device,such as a server, in communications with the client 102. The clientagent 120 and/or interceptor 350 may be installed and/or executed on theclient 102 in a manner without modification of an application. In someembodiments, the user of the client 102 or a computing device incommunications with the client 102 are not aware of the existence,execution or operation of the client agent 120 and/or interceptor 350.As such, in some embodiments, the client agent 120 and/or interceptor350 is installed, executed, and/or operated transparently to anapplication, user of the client 102, another computing device, such as aserver, or any of the protocol layers above and/or below the protocollayer interfaced to by the interceptor 350.

The client agent 120 includes an acceleration program 302, a streamingclient 306, a collection agent 304, and/or monitoring agent 197. In oneembodiment, the client agent 120 comprises an Independent ComputingArchitecture (ICA) client, or any portion thereof, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla., and is also referred to as anICA client. In some embodiments, the client 120 comprises an applicationstreaming client 306 for streaming an application from a server 106 to aclient 102. In some embodiments, the client agent 120 comprises anacceleration program 302 for accelerating communications between client102 and server 106. In another embodiment, the client agent 120 includesa collection agent 304 for performing end-point detection/scanning andcollecting end-point information for the appliance 200 and/or server106.

In some embodiments, the acceleration program 302 comprises aclient-side acceleration program for performing one or more accelerationtechniques to accelerate, enhance or otherwise improve a client'scommunications with and/or access to a server 106, such as accessing anapplication provided by a server 106. The logic, functions, and/oroperations of the executable instructions of the acceleration program302 may perform one or more of the following acceleration techniques: 1)multi-protocol compression, 2) transport control protocol pooling, 3)transport control protocol multiplexing, 4) transport control protocolbuffering, and 5) caching via a cache manager. Additionally, theacceleration program 302 may perform encryption and/or decryption of anycommunications received and/or transmitted by the client 102. In someembodiments, the acceleration program 302 performs one or more of theacceleration techniques in an integrated manner or fashion.Additionally, the acceleration program 302 can perform compression onany of the protocols, or multiple-protocols, carried as a payload of anetwork packet of the transport layer protocol.

The streaming client 306 comprises an application, program, process,service, task or executable instructions for receiving and executing astreamed application from a server 106. A server 106 may stream one ormore application data files to the streaming client 306 for playing,executing or otherwise causing to be executed the application on theclient 102. In some embodiments, the server 106 transmits a set ofcompressed or packaged application data files to the streaming client306. In some embodiments, the plurality of application files arecompressed and stored on a file server within an archive file such as aCAB, ZIP, SIT, TAR, JAR or other archive. In one embodiment, the server106 decompresses, unpackages or unarchives the application files andtransmits the files to the client 102. In another embodiment, the client102 decompresses, unpackages or unarchives the application files. Thestreaming client 306 dynamically installs the application, or portionthereof, and executes the application. In one embodiment, the streamingclient 306 may be an executable program. In some embodiments, thestreaming client 306 may be able to launch another executable program.

The collection agent 304 comprises an application, program, process,service, task or executable instructions for identifying, obtainingand/or collecting information about the client 102. In some embodiments,the appliance 200 transmits the collection agent 304 to the client 102or client agent 120. The collection agent 304 may be configuredaccording to one or more policies of the policy engine 236 of theappliance. In other embodiments, the collection agent 304 transmitscollected information on the client 102 to the appliance 200. In oneembodiment, the policy engine 236 of the appliance 200 uses thecollected information to determine and provide access, authenticationand authorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 comprises an end-pointdetection and scanning mechanism, which identifies and determines one ormore attributes or characteristics of the client. For example, thecollection agent 304 may identify and determine any one or more of thefollowing client-side attributes: 1) the operating system an/or aversion of an operating system, 2) a service pack of the operatingsystem, 3) a running service, 4) a running process, and 5) a file. Thecollection agent 304 may also identify and determine the presence orversions of any one or more of the following on the client: 1) antivirussoftware, 2) personal firewall software, 3) anti-spam software, and 4)internet security software. The policy engine 236 may have one or morepolicies based on any one or more of the attributes or characteristicsof the client or client-side attributes.

In some embodiments, the client agent 120 includes a monitoring agent197 as discussed in conjunction with FIGS. 1D and 2B. The monitoringagent 197 may be any type and form of script, such as Visual Basic orJava script. In one embodiment, the monitoring agent 129 monitors andmeasures performance of any portion of the client agent 120. Forexample, in some embodiments, the monitoring agent 129 monitors andmeasures performance of the acceleration program 302. In anotherembodiment, the monitoring agent 129 monitors and measures performanceof the streaming client 306. In other embodiments, the monitoring agent129 monitors and measures performance of the collection agent 304. Instill another embodiment, the monitoring agent 129 monitors and measuresperformance of the interceptor 350. In some embodiments, the monitoringagent 129 monitors and measures any resource of the client 102, such asmemory, CPU and disk.

The monitoring agent 197 may monitor and measure performance of anyapplication of the client. In one embodiment, the monitoring agent 129monitors and measures performance of a browser on the client 102. Insome embodiments, the monitoring agent 197 monitors and measuresperformance of any application delivered via the client agent 120. Inother embodiments, the monitoring agent 197 measures and monitors enduser response times for an application, such as web-based or HTTPresponse times. The monitoring agent 197 may monitor and measureperformance of an ICA or RDP client. In another embodiment, themonitoring agent 197 measures and monitors metrics for a user session orapplication session. In some embodiments, monitoring agent 197 measuresand monitors an ICA or RDP session. In one embodiment, the monitoringagent 197 measures and monitors the performance of the appliance 200 inaccelerating delivery of an application and/or data to the client 102.

In some embodiments and still referring to FIG. 3, a first program 322may be used to install and/or execute the client agent 120, or portionthereof, such as the interceptor 350, automatically, silently,transparently, or otherwise. In one embodiment, the first program 322comprises a plugin component, such an ActiveX control or Java control orscript that is loaded into and executed by an application. For example,the first program comprises an ActiveX control loaded and run by a webbrowser application, such as in the memory space or context of theapplication. In another embodiment, the first program 322 comprises aset of executable instructions loaded into and run by the application,such as a browser. In one embodiment, the first program 322 comprises adesigned and constructed program to install the client agent 120. Insome embodiments, the first program 322 obtains, downloads, or receivesthe client agent 120 via the network from another computing device. Inanother embodiment, the first program 322 is an installer program or aplug and play manager for installing programs, such as network drivers,on the operating system of the client 102.

D. Load Balancing with Metrics Selected by a User from ApplianceDetermined Metrics and/or Metrics Collected from a Device Via a NetworkManagement Protocol

Referring now to FIGS. 4A and 4B, systems and methods are depicted forload balancing based on metrics determined by the appliance 200 and/ormetrics collected by the appliance from a device or service via anetwork management protocol, such as a Simple Network ManagementProtocol (SNMP). The appliance provides a load monitor to monitor theload of one or more services 270 a-270 n. In one embodiment, a user mayconfigure one or more load monitors based on metrics selected from acustom metric table which includes metrics or objects obtains via anetwork management protocol query. In another embodiment, a user mayconfigure one or more load monitors based on metrics or parameterscollected by the appliance. In some embodiments, the user configures oneor more load monitors based on metrics selected from the custom metrictable and the appliance collected metrics. In response to the user'sselection, the appliance determines the load of the one or more servicesand load balances client requests to the services using any type of loadbalancing technique.

Referring now to FIG. 4A, an embodiment of an appliance for loadbalancing one or more services is depicted. In brief overview, anappliance 200 has one or more virtual servers, or vServers 275A-275Nconfigured to provide load balancing 284 to one or more services 270a-270 n deployed on or provided by one or more servers 106 a-106 b. AvServer 275A is associated with, configured to or bound to a service270A or a group of services 270A-270N. The appliance 200 has one or moreload monitors 405A-405N to monitor a status, operation, and/orperformance of the services 270A-270N. A load monitor is associatedwith, configured to or bound to a service 270A or a group of services270A-270N. The load monitors 405A-405B provide information to thevServers 275A-275N to determine which of the services 270A-270N shouldreceive a request received by a vServer 275. A load monitor 405 and/orvServer 275 may use appliance collected metrics 410 and/or deviceprovided metrics 420 to determine a load across a plurality of services270A-270N and to load balancing incoming client requests. The appliance200 also includes a configuration interface 435 to receive informationidentifying user selected or user defined metrics 430 to be used by theload monitors 405 and/or vServers 275 for load balancing the pluralityof services 270A-270N.

The appliance 200 may include any type and form of load monitor405A-405N, also referred to as monitoring agent, for monitoring anyoperational or performance characteristic or metric of a service 270,server 106 or device 100. A load monitor 405 may include software,hardware, or any combination of software and hardware. The load monitor405 may include any application, program, script, service, daemon,process, task, thread or set of executable instructions. In oneembodiment, the load monitor 405 operates or executes in kernel space ofthe appliance 200. In another embodiment, the load monitor 405 operatesor executes in user or application space of the appliance 200. In someembodiments, a first portion of the load monitor 405 operates in kernelspace while a second portion of the load monitor 405 operates inapplication layer or space of the appliance 200.

In one embodiment, the load monitor 405 communicates with a service 270once. In some embodiments, the load monitor 405 monitors or communicateswith a service 270 on a predetermined frequency, such as every 1 msec or1 sec. A user may configure or specify the predetermined frequency viathe configuration interface 425. In other cases, another appliance orsystem may configure or specify the predetermined frequency via theconfiguration interface 425. In yet another embodiment, the load monitor405 monitors or communicates with a service 270 responsive to one ormore events, such as receipt of a request, response or a network packet.In one embodiment, a load monitor 405 monitors or communicates with aservice 270 responsive to one or more policies of a policy engine.

In some embodiments, a load monitor 405 may use a request/replymessaging mechanism or protocol with the service 270 or server 106. Inother embodiments, a load monitor 405 may have a custom or proprietaryexchange protocol for communicating with a service, server or device. Inone embodiment, a load monitor 405 may use the protocol of the service270 to monitor or communicate with the service 270. As such, in someembodiments, the load monitor 405 uses the HTTP protocol to monitor orcommunicate with a web service 270A or an FTP protocol for an FTP server270B. In yet other embodiments, the load monitor 405 uses a TCP or ICMPprotocol for monitoring a service 270. In some embodiments, the loadmonitor 405 uses a network management protocol to monitor or query astatus or metric of a service, server or device. In one embodiment, theload monitor 405 uses a Simple Network Management Protocol (SNMP). Inanother embodiment, the load monitor 405 uses a common managementinformation protocol (CIMP).

In some embodiments, a single load monitor 405 monitors a plurality ofservices 270A-270N, or servers 106A-106B. In other embodiments, aplurality of load monitors 405A-405N monitor a single service 270A orserver 106A. In still other embodiments, multiple load monitors 405 mayeach monitor a plurality of services 270A-270N, or servers 106A-106N. Inone embodiment, multiple load monitors 405 may each monitor a service270. In yet another embodiment, a load monitor 405A may monitor one ormore other load monitors 405B-405N.

In some embodiments, the one or more load monitors 405 are associatedwith one or more services 270. In one embodiment, a user specifies orconfigures a load monitor 405 for one or more service 270 via theconfiguration interface 425. For example, a user via the configurationinterface 435 may issue a command to bind the monitor 405 to a service275. In other embodiments, the load monitor 405 is associated with avServer 275. In one embodiment, a user specifies or configures via theconfiguration interface 425 a load monitor 405 for a vServer 275. In yetanother embodiment, a use specifies or configures via the configurationinterface 425 a vServer 275 for one or more services 270A-270N. Forexample, a user may bind a vServer 275 to a service 270.

In some embodiments, the one or more load monitors 405 may monitor anappliance 200, vServer 275, network service 270, client 102, server 106,device 100 or any other network resource. In one embodiment, a userspecifies a type of network service to associate with the one or moremonitoring agents 405. In another embodiment, a user customizes amonitoring agent. For example, a user may implement or otherwise providea script for monitoring a service. In still another embodiment, ageneric monitoring agent 405 is used. In some embodiments, a monitoragent 405 is configurable to use a predetermined monitor, script orstatus message based on a type of protocol or type of service

In yet another embodiment, the one or more monitoring agents 405determine the response time of the one or more network services 270 forresponding to a request of one of the following types: ping, transportcontrol protocol (tcp), tcp extended content verification, hypertexttransfer protocol (http), http extended content verification, hypertexttransfer protocol secure (https), https extended content verification,user datagram protocol, domain name service, and file transfer protocol.In some embodiment, a monitoring agent 405 checks for predeterminedstatus codes in responses from the service 270. In other embodiments,the monitoring agent 405 checks for predetermined string patters inresponse from the service 270.

In some embodiments, the one or more load monitors or monitoring agents405 are protocol-specific agents. For example, an agent 405 maydetermine availability for a network service of a particularprotocol-type. In some embodiments, a monitoring agent 405 determines aresponse time of a server 106 or network service 270 to a TCP request.In one of these embodiments, the agent uses a “TCP/ICMP echo request”command to send a datagram to the network service 270, receive adatagram from the network service 270 in response, and determine aresponse time based on the roundtrip time of the datagram. In another ofthese embodiments, the monitoring agent 405 verifies that the responsefrom the network service 270 included expected content. In oneembodiment, the monitoring agent 405 verifies that the response did notinclude an error.

In other embodiments, a monitoring agent 405 determines availability ofa network service 270 to a UDP request. In one of these embodiments, theagent uses a “UDP echo” command to send a datagram to the networkservice 270, receive a datagram from the network service 270 inresponse, and determine a response time based on the roundtrip time ofthe datagram. In another of these embodiments, the monitoring agent 405verifies that the response from the network service 270 includedexpected content and did not contain errors.

In still other embodiments, the monitoring agent 405 determinesavailability of a network service 270 to an FTP request. In one of theseembodiments, the monitoring agent 405 sends an FTP command, such as a“get” command or a “put” command, to the network service 270 anddetermines a time needed by the network service 270 to respond to thecommand. In another of these embodiments, the monitoring agent 405verifies that the response from the network service 270 includedexpected content, such as contents of a file requested by a “get”command, and did not contain errors.

In yet other embodiments, the monitoring agent 405 determinesavailability of a network service 270 to an HTTP request. In one ofthese embodiments, the monitoring agent 405 sends an HTTP command, suchas a “get” request for a uniform resource locator (URL) or a file, tothe network service 270 and determines a time needed by the networkservice 270 to respond to the request. In another of these embodiments,the monitoring agent 405 verifies that the response from the networkservice 270 included expected content, such as the content of a web pageidentified by a URL. In some embodiment, the monitor agent 405 checksfor a predetermined status code. In other embodiments, the monitoringagent 405 checks for a predetermine string pattern in an HTTP response.

In further embodiments, the monitoring agent 405 determines availabilityof a network service 270 to a DNS request. In one of these embodiments,the monitoring agent 405 sends a DNS request, such as a dnsquery ornslookup for a known network address, to the server 106 or networkservice 270 and determines a time needed by the server 106 or networkservice 270 to respond to the request. In another of these embodiments,the monitoring agent 405 verifies that the response from the networkservice 270 included expected content, such as the domain name of acomputing device 100 associated with the known network address. In oneembodiment, monitoring agent 405 verifies the response did not have anerror.

In some embodiments, the appliance 200 via a monitoring agent 405identifies and collects metrics 410 based on network traffic andinformation traversing the appliance, or otherwise referred to asappliance collected parameters or metrics. The appliance 200 or agent405 may store the appliance collected metrics 410 in any type and formof data storage mechanism in memory and/or disk storage. In oneembodiment, the appliance stores the metrics 410 in a table. In anotherembodiment, the appliance stores the metrics 410 in a database. In yetanother embodiment, the appliance stores the metrics 410 in an object ordata structure. In still other embodiments, the appliance 200 storesappliance collected metrics 410 in multiple tables and/or data storagemechanisms. In one embodiments, the appliance collected metrics 410 maybe arranged or organized in any manner in the multiple tables.

In some embodiments, the monitoring agent 405 determines one or moremetrics 410 from network packets received and transmitted by theappliance. In one embodiment, the monitoring agent 405 determines anumber and/or type of connections to one or more services 270 or server106. In another embodiment, the monitoring agent 405 determines a numberof packets transmitted to a service 270 or server 106. In otherembodiments, the monitoring agents 405 determines a number of packetsreceived from or transmitted by a service 270 or server 106. In someembodiments, the monitoring agent 405 determines a response time from aservice 270 or service. In one embodiments, the monitoring agent 405determines an average response time. In another embodiment, themonitoring agent 405 determines a number or percentage of loss packets.In other embodiments, the monitoring agent 405 determines a number oferrors received from a service or server.

In some embodiments, the monitoring agent 405 determines a bandwidth ofa connection to a service 270 or a server 106. In one embodiment, themonitoring agent 405 determines the bandwidth of a connection based on aresponse time and/or packet loss. In another embodiment, the monitoringagent 405 determines the bandwidth of a connection based on a number ofbytes transferred or communicated to and/or form a service 270 or server106. In one embodiment, the monitoring agent 405 determines thebandwidth based on a number of bytes received from a service or serverover a predetermined time period, such as per second. In anotherembodiment, the monitoring agent 405 determines the bandwidth based on anumber of bytes transmitted to a service or server over a predeterminedtime period. In some embodiments, the monitoring agent 405 determinesthe bandwidth based on a number of bytes transmitted to and receivedfrom a service or server over a predetermined time period.

In some embodiments, the appliance 200 via a monitoring agent 405identifies and collects metrics 430 provided by a service, server ordevice. These metrics 430 may also be referred to as custom metrics or acustom metric table. The appliance 200 or agent 405 may store theservice or device collected metrics 430 in any type and form of datastorage mechanism in memory and/or disk storage. In one embodiment, theappliance stores the metrics 430 in a table. In another embodiment, theappliance stores the metrics 430 in a database. In yet anotherembodiment, the appliance stores the metrics 430 in an object or datastructure. In some embodiments, the appliance stores the metrics 430 inthe same data storage mechanism as the appliance collected metrics 410.In other embodiments, the appliance stores the metrics 430 in adifferent storage mechanism as the appliance collected metrics 410. Instill other embodiments, the appliance 200 stores device providedmetrics 420 in multiple tables and/or data storage mechanisms. In oneembodiments, the device provided metrics 420 may be arranged ororganized in any manner in the multiple tables. For example, theappliance 200 may maintain a metrics table 420 for each service, deviceor application.

In one embodiment, the load monitor 405 uses a network managementprotocol, such as SNMP, to query a server or device for one or moreobjects identifiers and data for the objects of the object identifiers.By way of example only and not in any way limiting, the load monitor 405uses an SNMP architecture to provide management information bases (MIBs)417, which specify management data of a device or device subsystem, suchas a service 270, using a hierarchical namespace containing objectidentifiers 422A-422N for managed objects. In some embodiments, a MIB417 is a collection of information that is organized hierarchically.MIBs 417 may be accessed using a network-management protocol such asSNMP. An MIB 417 includes managed objects identified by objectidentifiers 422A-422N. In one embodiment, a managed object (sometimescalled a MIB object, an object, or a MIB) is one of any number ofcharacteristics or metrics of a managed device, appliance or system. Insome embodiments, a managed objects includes one or more objectinstances, which correspond to or referred to as variables.

In one embodiment, the MIB 417 hierarchy may be depicted as a tree witha nameless root, the levels of which are assigned by differentorganizations. In some embodiments, the top-level MIB object IDs maybelong to different standards organizations, while lower-level objectIDs are allocated by associated organizations. The MIB 417 and/orobjects 422A-422N may be arranged, constructed or organized formanagement across any of layers of the OSI reference model. In someembodiments, the MIB 417 and/or objects 422A-422N provide managed dataand information on applications such as databases, email, and webservices. Furthermore, the MIB 417 and/or objects 422A-422N may definefor any area-specific or appliance specification information andoperations, such as for any type of service 270, server 106 or device100 load balanced or managed by the appliance 200.

In the example embodiment of SNMP, the SNMP communication model is basedon a manager 415 and an agent 416 with a data of management information417 and management objects 422A-422N. In one embodiment, the manager 415provides an interface between appliance and the managed system. Theagent 416 provides the interface between the manager 415 and the device,system, application, component, element or resource being managed. Asillustrated in FIG. 4A, the appliance 200 may include a manager 415which requests and obtains object identifiers and values from an agent416, such as the agent 416 on a server 106. In the example of SNMP, amanager 415 communicates a GET or GET-NEXT message to requestinformation for a specific object. The agent 416, in response to themanger's request, issues a GET-RESPONSE message to the manager 415 withthe information requested or an error message. The manager 415 maytransmit a SET message to request a change to a value of a specificvariable or object 422. The agent 416 may issue a TRAP message to informthe manager 415 of an event, such as an alarm or error on a service 270.

Although generally described in an embodiment of an SNMP networkmanagement protocol, the appliance 200 and/or load monitor 405 may useany type and form of network management protocol and communication modelto obtain identifiers and values of information, such as objects orvariables, from another device for a managed system, sub-system orservice 270. For example, the appliance 200 may use any of the followingprotocols and/or communication models: Remote monitoring (RMON), AgentX,Simple Gateway Monitoring Protocol (SGMP), Common management informationprotocol (CMIP), Common management information service (CMIS) or CMIPover TCP/IP (CMOT).

Furthermore, although a MIB 417 is generally described in reference to amanager/agent communication model for an example network managementprotocol such as SNMP, the MIB 417 may include any type and form of datastorage of object identifiers, variables, parameters or otheridentifiers of metrics. The MIB 417 may be either protocol dependent orprotocol independent. For example, the MIB 417 may comprise a table ofmetrics for a device or service that can be queried via any type andform of API.

The managed objects or variables provided via the network managementprotocol may provide any type and form of metrics or operationalcharacteristics of the service, server or device to be used by theappliance for load balancing, or any other function of the appliance200. In one embodiment, the device provided metrics 420 may include anyof the metrics 410 collected by the appliance as described above. Inanother embodiment, the device provided metrics 420 may include any typeand form of information on any resource usage of the managed device,service or system. In one embodiment, the metrics 410 include CPU,memory and/or disk usage of the device and/or service 270. In otherembodiments, the metrics 420 may include information on a number ofconnections, sessions or clients of the service 270. In someembodiments, the metrics 420 include any information on any thresholdsof the service 270 or server 106, such as a threshold identifying amaximum number of sessions or clients. In yet another embodiment, themetrics 420 include any information on a type of protocol of the service270. In other embodiments, the metrics 420 include any information onany alarms or errors of the service 270.

In some embodiments, each load monitor 405 includes the appliancecollected metrics 410. For example, the metric table 410 may beimplicitly bound to each monitor 405 by default. In other embodiments, auser associates or binds a custom metric table 420 to a monitor 405. Inyet another embodiment, a user associates or binds a custom metric table420 and appliance collected table 410 to a monitor 405. In yet otherembodiments, a user may associate or bind any combination of one or moreappliance collected metric tables 410 and custom metric tables 420 toone or more load monitors 405.

In some embodiments, a user via the configuration interface 425 mayconfigure or specify for a load monitor 405 one or more objectidentifiers 422A-422N to obtain values for and store in the metrics 420.For example, the user may specify a user-defined metric 430. In otherembodiments, the appliance 200 or load monitor 405 obtains a list of oneor more object identifiers 422A-4222N from a device 100, such as server106 or service 270. In yet another embodiment, the appliance 200includes one or more metric tables 420 with predetermined OIDS 422A-422Nfor a known device. For example, the appliance 200 may include a metrictable 420 for any one or more of the following appliances or devices: 1)any version of the NetScaler device manufactured by Citrix Systems, Inc.of Ft. Lauderdale, Fla.; 2) any of the appliances, such as BIGIP orWebAccelerator, manufactured by F5 Networks, Inc. of Seattle, Wash.; 3)any of the AppDirector or AppXcel devices manufactured by Radware Ltd ofMahwah, N.J.; 4) any application acceleration and/or security relatedappliances and/or software manufactured by Cisco Systems, Inc. of SanJose, Calif.

The appliance 200, vServer 275 and/or load monitor 405 computes,calculates or otherwise determines a load 440 for each service 270 basedon any of the metrics from the appliance collected metrics 410 and/ordevice provided metrics 420. The appliance 200 may use a weight435A-435N and a threshold 437A-437N for each of the metrics used in thedetermination of the load 440. In one embodiment, the appliance 200establishes a weight 435 and/or a threshold 437. In other embodiments, auser establishes a weight 435 and/or a threshold 437. For example, insome cases, if a user does not specify a weight for a plurality ofmetrics, the appliance equally weights each metric. In one exampleembodiment, the appliance 200 determines the load 440 for each serviceas follows:

Sum(weight of metric/established ceiling value of metric)*(obtainedvalue of metric/established ceiling value of metric))/Sum(weights))

In some embodiments, a metric value may be based on a range of 0-100, orabsolute range. In other embodiments, a metric value may not be based ona range of 0-100 or is otherwise relative to the type of metric andpossible range of values. For example, a metric identifying a number ofconnections may have a ceiling or predetermined maximum value of 10,000.In one of these embodiments, the appliance establishes a ceiling valueor predetermined upper limit for the metric value. In another of theseembodiments, a user via the configuration interface 425 establishes aceiling value or predetermined upper limit for the metric value. Infurther embodiments, the established ceiling value may comprise a valueless than the actual maximum value for the metric or upper limit of therange value. For example, a user may specify or configure a relativerange value based on a desired operational or performance range of ametric.

In some embodiments, if a metric of a service exceeds a user orappliance provided threshold, the service may be excluded from the loaddetermination or otherwise from a load balancing decision. In otherembodiments, if all the metrics of a service exceeds their correspondingthresholds, the service may be excluded from the load determination orotherwise from a load balancing decisions. In yet another embodiment,even if a service exceeds the threshold(s) for one or more of themetrics, the service may be considered in the load determination orotherwise for load selection. In some cases, a client session may beidentified as persistent or sticky to a vServer 275 or service 270. Inthese cases, if a request for the client's sessions is received by theappliance, the appliance may provide the request to a vServer 275 orservice 270 although a metric for the vServer or service has beenexceeded.

In still other embodiments, if a threshold of a metric of a service orvirtual server has been exceeded, the appliance may, in response to thethreshold being exceeded, redirect the client making the request toanother resource. In one embodiment, the appliance may transmit a URL tothe client comprising the address of a server 106 or service 270 suchthat the client may bypass the appliance 200 and access the server 106or service 270 directly. In one embodiment, the appliance may transmit aURL to the client comprising the address of a second appliance 200 oranother device. In still another embodiment, the appliance 200 mayredirect the client request to a second appliance, device, service orserver on behalf of the client.

In some embodiments, if a threshold of a metric of a service or virtualserver has been exceeded, the appliance may, in response to thethreshold being exceeded direct a client request to a second virtualserver or service. In one embodiment, a second virtual server may be abackup to a primary virtual server. Upon detection of the thresholdbeing exceeded, the appliance may spillover requests and connections toa second virtual server.

Although the load 440 is generally discussed in view of the aboveequation, the appliance may use any type and form of load calculation,weighted or not weighted. In some embodiments, the appliance 200determines the load using an average of metric values. In otherembodiments, the appliance 200 determines the load 440 using anyderivative value of a metric. In another embodiment, the appliance 200determines the load 440 using any statistical measure of a metric. Instill another embodiment, the appliance 200 determines the load 440using any function or computation of a metric. In yet other embodiments,the appliance 200 may determine a load 440 for each metric. In theseembodiments, the appliance 200 may aggregate, compare or otherwisecompute an load 440 based on any type and form of aggregation of ametric's contribution to a load of a service.

In some embodiments, a user configures multiple monitors 405 for aservice 270. In these embodiments, the load 440 on the service 270 is asum of the load of all the monitors. In one embodiment, the sum of theload from multiple monitors 440 is weighted. The appliance may assign amonitoring 405 a weight. A weight may comprise an integer, decimal, orany other numeric indicator. In some embodiments, a user may configurevia the configuration interface 425 the weight corresponding to amonitor 405. In some embodiments, all monitors 405 may be assigned equalweight. In other embodiments, a plurality of monitors 405 may each beassigned different weights. The weights may be assigned to the monitorsbased on any criteria indicating relative importance, including withoutlimitation the appliance or user determination of the relativeimportance or value of the monitor in view of the service, reliabilityof the monitoring mechanism, and the frequency of monitoring.

In one embodiment, a monitoring agent 405 may be assigned a weight basedon the relative importance of the service monitored by the appliance.For example, if most user requests in an environment are HTTP requests,a monitoring agent monitoring HTTP availability of a server 106 might beassigned a weight of 10, while a monitoring agent monitoring FTPavailability of a server 106 might be assigned a weight of 3. Or, forexample, if an administrator placed a high priority on UDP applications,a monitoring agent monitoring UDP availability of a server may beassigned a weight of 20, while a DNS monitoring agent may be assigned aweight of 5.

In some embodiments, an appliance 200 may compute a sum of the weightsof the monitoring agents currently reporting a network service 270 asoperational. For example, if five monitoring agents, each assigned aweight of 30, are monitoring a network service 270, and three of thefive monitoring agents report the network service 270 as available, theappliance may determine the sum of the monitoring agents currentlyreporting the network service 270 as operational to be 90. Or forexample, if only two monitoring agents, one with a weight of 20 and theother with a weight of 40, are reporting a server 106 as available, theappliance may compute the sum of the monitoring agents currentlyreporting a server 106 as operational to be 60.

The appliance 200 also includes a configuration interface 425 providingany type and form of interface mechanism for a user, application orsystem to communicate with the appliance 200. In one embodiment, theconfiguration interface 425 includes a command line interface 425B. Inanother embodiment, the configuration interface 425 includes a graphicaluser interface 425A. In some embodiments, the configuration interface425 includes an application programming interface (API) or developmenttoolkit for an application, program or script to communicate with theappliance 200.

In some embodiments, the appliance 200 displays the configurationinterface 425 via a display of the appliance. In other embodiments, aconfiguration terminal or device 100 connects to or communicates withthe appliance 200 and displays the configuration interface 425. Forexample, the configuration device 100 or terminal may connect to theappliance 200 via a port and IP address of the appliance 200. Theappliance 200 may provide a web service listening on the port and IPaddress to serve a page to the user. The served page may provide a userinterface for configuring the appliance 200. In other embodiments, theconfiguration terminal 100 may connect and communicate with theappliance 200 via any type and form of connection, including a monitorport, serial port or USB connection.

Via the configuration interface 425, the appliance 200 may receiveinformation identifying user selected metrics 430 to use in determiningthe load 440 for one or more services. In one embodiment, the useridentifies or selects a metric from a plurality of appliance collectedmetrics 410. In another embodiment, the user identifies or selects ametric from a plurality of device provided metrics 420. In someembodiments, the user selects one or more metrics from the appliancecollected metrics 510 and one or more metrics from the device providedmetrics 410. The appliance 200 may also receive via the configurationinterface 425 information identifying a user's selection or designationof a weight 435 for a metric. For example, a user may provide a value ofa weight 435 for a metric. In some embodiments, the appliance 200receives information identifying a user provided value for a threshold437.

In operation, the appliance 200 may use user selected metrics 430 anduser provided weights 435 and thresholds 437 for determining the load440. In another embodiment, the appliance may use any applianceestablished metrics from the appliance collected metrics 410 fordetermining the load. In one embodiment, a user establishes a weightand/or a threshold for an appliance provided metric. So although themetric may not be user selected in some embodiments, the user maycontrol or configure the weights 435 and/or thresholds 437 for themetrics 410. In other embodiments, the appliance may use any combinationof user selected metrics 430 and appliance established metrics 410 fordetermining the load. In another embodiment, the appliance 200 may useany combination of user provided weights 435 and/or thresholds 437 andappliance provided weights 435 and/or thresholds 437 for any metric usedfor determining the load 440.

Referring now to FIG. 4B, an embodiment of steps of a method for loadbalancing one or more services is depicted. In some embodiments, theappliance 200 may load balance one or more services using appliancecollected metrics 410 and device provided metrics 420. In otherembodiments, the appliance 200 load balances one or more services basedon user selected metrics, weights and/or thresholds. In brief overview,at step 455 of method 450, multiple metrics are identified for loadbalancing a plurality of services 270A-270N by the appliance 200. Atstep 457, in some embodiment, the appliance 200 receives user definedmetrics to collect or monitor for a service 270. At step 460, theappliance receives user selected metrics from the set of identifiedmetrics. The user may also identify weights and/or thresholds for themetric. At step 465, the appliance determines a load for each of theservices based on the user selected metric information. At step 470, theappliance receives a client request to access a service. At step 475,based on the load determination, the appliance determines a service fromthe plurality of services to transmit or forward the client request. Atstep 480, the appliance transmits the client's request to the applianceselected service.

In further details, at step 455, the appliance 200 identifies metrics tocollect and monitor for load balancing one or more services 270A-270N.In one embodiment, the appliance 200 provides or identifies one or moreappliance collected metrics 410. For example, a table 410 may identifymetrics collected by the appliance 200. In another embodiment, theappliance 200 provides one or more predetermined tables of deviceprovided metrics 420, such as for an appliance of Citrix, F5, Cisco, orRadware. In other embodiments, the appliances 200 identifies one or moremetrics to collect via a network management protocol in an object orvariable database, such as an MIB 417 for SNMP. In one embodiment, theappliance provides a preconfigured or preinstalled MIB 417 for apredetermined device or service 270, such as an application.

In some embodiments, the appliance 200 queries a device or service 270to determine available metrics to collect and/or monitor. For example,in one embodiment, the appliance 200 queries a device or service foravailable object identifiers 422A-422N. In another embodiment, theappliance 200 uses a network management protocol, such as SNMP, to queryfor the identification of objects in a MIB 417. In yet anotherembodiment, a user via the configuration interface 425 identifies one ormore object identifiers 422A-422N to collect and/or monitor from adevice or service 270, such as an application.

In some embodiments, at step 457, a user specifies or defines a metricfor the appliance to collect and/or monitor for a service 270. Forexample, the user may specify via the configuration interface 425 anobject identifier in a MIB 417. In other embodiments, a user mayconfigure or implement a load monitor 405 to collect and/or monitor auser-defined or specified metric. In yet another embodiment, a user,such as a network administrator, may configure, specify or implement oneor more object identifiers 422 in a MIB 417 deployed on a server 106. Insome embodiments, the user may implement an application, program,script, service or other set of executable instructions to collectmetrics on the server 106 and store values for the metrics in the MIB417 on the server 106. For example, the user may execute a program orscript to monitor metrics of a service 270 on the server 106 and updatethe MIB 417 with the collected values. The manager 415 on the appliance200 may query the agent 416 on the server for information and/or valuesof the metrics stored in the server's MIB 417 for the service 270.

At step 460, the appliance 200 receives information identifying aselection by a user of one or more metrics identified via the appliance.In some embodiments, a user via the configuration interface 425 selectsone or more metrics provided via the appliance 200 to use for loadbalancing a server 270. In one embodiment, the appliance 200 providesfor selection by the user via the configuration interface 425 any one ormore of the appliance collected metrics 410 or device provided metrics420. A user may configure the appliance 200 via a command line interface425B or graphical user interface 425A to use one or more user selectedmetrics 430 for determining a load 440 or otherwise for load balancingservices 270A-270N by the appliance 200.

In one embodiment, the appliance 200 receives information identifyingthat the user selected one or more appliance collected metrics 410. Inanother embodiment, the appliance 200 receives information identifyingthat the user selected one or more device provided metrics 420. In yetanother embodiment, the appliance 200 receives information identifyingthat the user selected one or more appliance collected metrics 410 andone or more device provided metrics 420.

Furthermore, via the configuration interface 425, the appliance 200 mayreceive information identifying a user's designation or establishment ofa weight 435 for a metric. In one embodiment, the appliance 200 receivesa user's identification of a weight 435 for a user selected metric 430.In another embodiment, the appliance 200 receives a user'sidentification of a weight 435 for an appliance established metric 410.In other embodiments, the appliance 200 may receive informationidentifying a user's designation or establishment of a threshold 437 fora metric. In one embodiment, the appliance 200 receives a user'sidentification of a threshold 437 for a user selected metric 430. Inanother embodiment, the appliance 200 receives a user's identificationof a threshold 437 for an appliance established metric 410.

At step 465, the appliance determines a load for each of the one or moreservices. In one embodiment, a load monitor 405 collects and/or monitorsone or more of the user selected metrics 430 for a service. In anotherembodiment, the load monitor 405 collects and/or monitors appliancecollected metrics 410. In some embodiments, a load monitor 405 collectsmetrics via a network management protocol, such as SNMP. In yet anotherembodiment, multiple load monitors 405A-405N collect and/or monitormetrics for a service 270. In one embodiment, although a user selectedone or more metrics 430 for collecting and/or monitoring a service 270,the appliance 200 collects and monitors any one or more applianceestablished metrics 410, such as number of connections, response time,bandwidth, and number of packets, for the service 270.

In some embodiments, a vServer 275 determines the load 440 for eachservice 270 via metric information collected and monitored by a loadmonitor 405. In another embodiment, the load monitor 405 determines theload 440 for the service 270 being monitored. The appliance 200 and/orload monitor 405 may determine the load 440 using a user selected metric430 weighted by a user designated weight 435. In some embodiments, theappliance 200 and/or load monitor 405 determines the load 440 using aplurality of user selected metrics 430 weighted by user designatedweights 435. In yet another embodiment, the appliance 200 and/or loadmonitor 405 determines the load using a user selected metric 430 anduser identified weight 435 and an appliance established metric 410 andan appliance established weight 435. In further embodiments, theappliance 200 determines the load 440 by summing a weighted load foreach metric (user and/or appliance) used for the service 270. For theembodiment of multiple monitors 405A-405N per service 270, the appliance200 may determine the load for the service by assigning a weight to eachmonitor and computing weighted load across all the monitors 405. Inother embodiments, the appliance 200 and/or load monitor 405 determinesa load for a service 270 at a predetermined frequency, such as every 1msec. or every 1 sec.

In some embodiments, a load monitor 405 determines that a metric for aservice 270 has reached or exceed a threshold 437. In other embodiments,a load monitor 405 determines that a metric for a service 270 is withina threshold 437. In one embodiment, the load monitor 405 uses anappliance established or provided threshold for a metric. In anotherembodiment, the load monitor 405 user a user specified or configuredthreshold 437.

At step 470, the appliance 200 receives a request from a client toaccess a service. In one embodiment, a virtual server or vServer 275intercepts or otherwise receives a request from the client. In someembodiments, the virtual server 275 transparently intercepts theclient's request to a service 270 or server 106. In other embodiments, aclient 102 transmits the request to the vServer 275. In anotherembodiment, the vServer 275 determines from the request that the requestis for one or more services under management by the appliance 200. Inone embodiment, the vServer 275 intercepts or receives the request via aSSL VPN connection between the client and the appliance 200.

At step 475, the appliance 200 determines which of the services todirect the client request based on determination of the load 440 foreach service 270. In one embodiment, the vServer 275 directs the requestresponsive to one or more load monitors 405. In some embodiments, avServer 275 directs, forwards or otherwise transmits the request to aservice 270 with the least or smallest load. In one embodiment, thevServer 275 directs, forwards or otherwise transmits the request to aservice with one of the lower determined loads. In some embodiments, thevServer 275 directs, forwards or otherwise transmits the request to theservice previously handling requests from the client 102. In oneembodiment, the vServer 275 transmits the request to the previously usedservice if the load of the service is within a predetermined threshold.In some embodiments, the vServer 275 transmits the request to the firstavailable service in a list with a determined load within apredetermined threshold.

In another embodiment, a vServer 275 directs, forwards or otherwisetransmits the request to a service 270 using a round robin technique, orweighted round robin. In yet another embodiment, the vServer 275 directsthe request to a service based on one or more metrics, such as appliancecollected metrics 410 or device provided metrics 420. For example, insome embodiments, the vServer 275 directs the request to a service basedon one or more of the following: least response or round trip time,least number of connections, least number of packets, and leastbandwidth. In yet other embodiments, the vServer 275 directs the requestto a service based on one or more device provided metrics 430, such asCPU, memory and disk resource usage. In another example, the vServer 275directs the request to a service based on service resource usage on theserver, such as system resource usage by an application or session ofthe application.

In some embodiments, a vServer 275 may not direct a request to a service270 in which a metric for the service 270 has exceeded a threshold 437,such as a user configured threshold 437. In other embodiments, a vServer275 may not direct to a request to a service 270 if more than onethreshold 437 of the metrics for the service has been exceeded. In yetanother embodiment, a vServer 275 may direct a request to a service 270if a metric threshold 437 has been reached or exceeded. For example, ifone metric threshold 437 of a plurality of thresholds 437 has beenexceeded, then the vServer 275 may still direct the request to theservice if the other metric thresholds have not been reached.

In still other embodiments, the appliance 200 may determine from loadmonitoring that a metric of a first vServer 275A has reached a threshold437. In response to the determination, the appliance 200 may spillovermanagement of the services 270A-270N to a second virtual server, orvServer 275B. In one embodiment, the second virtual server 275B may be abackup server. In some embodiments, the second virtual server 275B isestablished in response to detecting the first virtual server 275A hasreached one or more thresholds. In another embodiment, the secondvirtual server 275B may be established and running on the appliance 200.

At step 480, the appliance transmits the client request to the servicedetermined by the appliance at 475. In one embodiment, the appliance 200transmits the client request in a manner transparent to the service 270such that the request appears to have been sent from the client insteadof the appliance 200. For example, the appliance 200 may act as atransparent or intercepting proxy for the client 102. In otherembodiments, the appliance 200 acts as a non-transparent proxy andtransmits the request to the service on the client's behalf. In someembodiment, the vServer 275 transmits the request to a service 270. Inother embodiments, a backup vServer 275 transmits the request to theservice. In yet other embodiments, a second vServer 275 transmits therequest to the service.

E. Global Server Load Balancing Among Heterogeneous Device

Referring now to FIGS. 5A-5C, systems and methods for load balancing aplurality of heterogeneous devices are depicted. The appliance 200described herein may be deployed to load balance a plurality of servicesand load balancing devices. A first appliance 200 may communicate with asecond appliance 200A of the same type via a predetermined metricexchange protocol (MEP). The first appliance 200 obtains via the MEPprotocol metrics to use for determining a load for the second appliance200A. Other devices of a different type than the first appliance may bedeployed in the network to perform local load balancing, such as for aserver farm. These devices may not communicate via the MEP protocol ofthe first appliance 200. Instead, these other device may provide metricsvia a network management protocol, such as a Simple Network ManagementProtocol (SNMP). Using the techniques described in conjunction withFIGS. 4A and 4B, the first appliance 200 obtains metrics from theseheterogeneous devices via the network management protocol. With metricsobtains via the MEP protocol from devices of the same type and metricsobtained via a network management protocol from device of a differenttype, the appliance 200 may uses these combined metrics to determine aload across these heterogeneous devices and to direct request to one ofthe devices based on the load.

Referring now to FIG. 5A, an example embodiment of a network environmentfor load balancing heterogeneous devices, including servers and local orother load balancing devices, is depicted. In brief overview, a networkenvironment includes a plurality of different types of load balancingdevices and servers. The appliance 200 is configured as a global loadbalancing device to load balance the plurality of load balancing devicesand servers. Each of the load balancing devices may perform local loadbalancing to one or more services 270A-270N. For example, a first set ofload balancing appliances 200A-200N of the same type may perform localload balancing of services or servers on a first network 104. Theseappliances 200A-200B may be of the same type of the global loadbalancing appliance 200. Or in some cases, local load balancingappliance 200A-200N are designed and constructed to communicate metricsand other information via a metric exchange protocol 540. A second typeof load balancing appliances 500A-500N may perform local load balancingfor one or more services 270A′-270N′ on a second network 104′. Theseload balancing appliances 500A-500N may be of a different type than thefirst type of appliance 200A-200N and/or the global load balancingappliance 200. The appliance 500A-500N may operate or execute one ormore virtual servers or vServers 275A-275N. Appliance 500A-500N may notbe designed to communicate via the MEP protocol 540 of appliances200-200N. Instead these appliances 500A-500N may provide metrics via anetwork management protocol, such as SNMP. The global load balancingappliance 200 may also perform load balancing for one or more servicesor servers, such as a server farm 38. Each of the servers or servicesmay be of a different type, such as an HTTP service and an FTP service.

In view of FIG. 5A, the plurality of appliances, servers, and servicesmay be deployed in a hierarchical fashion. The first appliance 200 maybe the global load balancing appliance at the top of the hierarchy tomanage a plurality of other appliances 200A-200N, 500A-500N and servers.In one case, the appliance 200 manages one or more servers 106 orservice 270A-270N directly. In another case, the appliance 200 managesone or more appliances 200A-200N, 500A-500N, which in turn manages oneor more servers 106 or services 270A-270N. An appliance managed by thefirst appliance 200 may manage a second appliance, which in turnsmanages one or more services or servers.

By way of example in view of various load balancing products, the globalload balancing appliance 200 may be any of the product embodimentsreferred to as NetScaler manufactured by Citrix Systems, Inc. Theappliances 200A-200N may also be a NetScaler device configured toperform local load balancing of one or more services 270A-270N. As theappliances 200A-200N are of the same type as the global load balancingappliance 200, these appliances are designed and constructed tocommunicate via a predetermine protocol or and/or communication modelreferred to as metric exchange protocol. The appliance 200A-200N may beconfigured to provide metric information at a predetermined frequency toappliance 200. One or more of the appliances 500A-500N may compriseanother type of load balancing device, such as a BigIP load balancingdevice manufactured by F5 Networks, Inc. Another one or more of theappliances 500A-500N may comprise a different type of load balancingdevice, such as the AppDirector appliance manufactured by Radware, LTD.In some cases, one or more of the appliances 500A-500N may comprise aCisco load balancing device. In other cases, one or more of theappliances 500A-500N may comprise a Nortel load balancing device. Anyone or more of these appliances 500A-500N may not be designed orconstructed to communicate with appliance 200 via the MEP protocol 540.Although the example is generally described above as Citrix NetScalerappliance 200 providing global load balancing device, any other type ofload balancing device may be used.

Instead of using MEP 540, each of these different appliances 500A-500Nmay provide metric information via a network management protocol, suchas SNMP. As illustrated in FIG. 5A, these appliances 500 may include anagent 416 for providing object identifiers 422A-422N via an MIB 417.Further to this example embodiment and as discussed in conjunction withFIGS. 4A and 4B, the appliance 200 using a manager/agent communicationmodel may query any of these appliances 500A-500N via a networkmanagement protocol to identify, collect and monitor objects identifiedvia the MIB 417. In some cases, the appliance 200 may use SNMP tocommunicate with one or more appliance 500A-500N. In other cases, theappliance 200 may use another type of network management protocol tocommunication another one or more of the appliances 500A-500N. In stillanother case, the appliance 200 may use a third type of network managerprotocol to communicate with a further set of one or more appliances500A-500N.

Appliances 200A-200N may be considered homogenous or the same type ofappliance or device as appliance 200. In one embodiment, the appliances200A-200N is the same product family of the appliance 200. In anotherembodiment, the appliance 200A-200N is a version of the same device ofthe appliance 200. In one case, the appliances 200 and 200A-220N aremanufactured by the same company. In some embodiments, the appliances200A-200N and appliance 200 are configured, designed and constructed tocommunicating using a predetermined protocol and/or communication model.In one embodiment, the appliances 200A-200N and appliance 200 areconfigured, designed and constructed to use a proprietary or customprotocol and/or communication model.

Appliances 500A-500N may be considered heterogonous or a different typeof appliance or device as appliance 200. In one embodiment, theappliances 500A-500N are manufactured by a different company thanappliance 200. In some embodiments, the appliances 500A-500N andappliance 500 are not specifically designed to communicate using apredetermined protocol and/or communication model. In one embodiment,the appliances 500A-500N and appliance 200 are not configured, designedand constructed to use a proprietary or custom protocol and/orcommunication model. In some cases, appliances 500A-500N use a networkmanagement protocol instead of using a proprietary protocol forproviding metrics to other devices, applications or services.

Referring now to FIG. 5B, an embodiment of the appliance 200 foridentifying, collecting and monitoring metrics obtained fromheterogeneous network devices and servers with a plurality of protocolsis depicted. The appliance 200 may have one or more virtual servers275A-275N configured, constructed or designed to provide load balancingof the plurality of devices over one or more networks 104, 104′, 104′.The appliance 200 may use one or more load monitors 405A-405N to monitorthe load of each of the heterogeneous devices. In one embodiment, theappliance 200 monitors the load of appliances 200A-200N. The appliance200 and/or load monitor 405 uses the MEP protocol 540 to obtain metricsfrom one or more of the appliances 200A-200N. In another embodiment, theappliance 200 monitors the load of appliance 500A-500N. In otherembodiments, the appliance 200 monitors the load of one or more serves106. In still another embodiment, the appliance 200 monitors the loadamong servers in a server farm 38. The appliance 200 may use one or morenetwork management protocols to obtain metrics from server 106, serverfarm 38, and appliances 500A-500N.

The appliance 200 collects metrics via the MEP protocol 540 and networkmanagement protocols from a wide variety of heterogeneous devices, suchas appliances 500A-500N and servers 106, and homogenous devices200A-220N. The appliance 200 stores the metrics in a GSLB (Global ServerLoad Balancing) or global metrics table 530 comprising any type and formof data storage element, such as a file, database, object or datastructure in memory and/or on disk. The vServers 275 and/or loadmonitors 405 use one or more of the metrics from the GSLB metrics 530 toprovide global load balancing of servers, server farms, virtual servers,and load balancing devices.

The appliance 200 may collect and monitor metrics obtained via a MEPprotocol 540 from one or more appliance 200A-200N and store them in aMEP based metrics table 510A-510N. In one embodiment, the appliance 200uses a first type or first version of a MEP protocol 540 to obtainmetrics from a first appliance 200A and stores the metrics in a firsttable 510A. In another embodiment, the appliance 200 uses a second typeor second version of a MEP protocol 540′ to obtain metrics from a secondappliance 200N and stores the metrics in a second table 510N.

The appliance 200 may collect and monitor metrics from appliances500A-500N using any type and form of network management protocol (NMP)and store the metrics in a NMP based metrics table 520A-520N. In oneembodiment, the appliance 200 uses a SNMP protocol and communicationmodel to obtains metrics from a second type of appliance 500A and storesthe metrics in a NMP based metric table 520A. In some embodiments, theappliances 200 uses a second type of network management protocol, suchas CIMP, to obtain from a second or third type of appliance 500N andstores the metrics in a NMP based metric table 520N. In someembodiments, appliance 500A is a different type of appliance thanappliance 500N but both appliances support the same network managementprotocol for providing metrics.

The appliance 200 may also collect and monitor metrics from a server 106and/or server arm 38 using any type and form of network managementprotocol (NMP) and store the metrics in a NMP based metrics table520A′-520N′. In one embodiment, the appliance 200 uses the same networkmanagement protocol, such as SNMP, for obtaining metrics from a server106 as used for obtaining metrics from one of the appliances 500A-500N.In another embodiments, the appliance 200 uses a different type ofnetwork management protocol for obtaining metrics from the server thanis used by the appliance 200 for obtaining metrics from an appliance500.

The appliance 200 may store metrics for the GSLB metrics 520 in aseparate table for each device. For example, the appliance 200 may storemetrics for a first appliance 200A in a first metrics table 510A, andmetrics from a second appliance 520A in a second metrics table 520A. Theappliance 200 may store metrics from a server 106 in a server metricstables 520A′. In another embodiment, the appliance 200 stores metricsfrom a server farm 38 to a metrics table 520N′ for the server farm.

The appliance 200 may store metrics for the GSLB metrics 520 in aseparate table for each type of protocol. For example, the appliance 200may store all MEP based metrics from a plurality of appliances 200A-200Nin a first metrics table. In some embodiments, the appliance 200 storesa first type or version of MEP protocol based metrics in a first table510A and a second type or version of an MEP protocol in a second table510N. The appliance 200 may store all SNMP based metrics from one ormore appliances 500A-500N in a second metrics table. In another example,the appliance may store metrics from a second type of network managementprotocol from one or more appliances 500A-500N to a third metrics table.

The GSLB metrics 530 may comprise any type and form of data, statistics,status or information related to or associated with the operationaland/or performance characteristics of the appliance 200, 500, a server106 or server farm 38. The global metrics 530 may comprise any type andform of data, statistics, status or information related to the networkof the appliance 200,500, and/or server 106 or server farm 38. Theglobal metrics 530 may comprise any type and form of data, statistics,status or information related to the services 270A-270N load balanced bythe appliance 200A-200N, 500A-500N. In some embodiments, the globalmetrics 530 comprises operational and/or performance data on any client102 and/or server 106 connected to the appliance 200A-200N, 500A-500N.In one embodiment, the appliance 200A-200N, 500A-500N determinesoperational and/or performance information about any client 102 orserver 106 it is connected to or servicing, and creates metrics on theseclients 102 and/or server 106. In this embodiment, the appliance200A-200N, 500A-500N may provide these metrics to the global loadbalancing appliance 200.

In some embodiments, the operational and/or performance characteristicprovides a metrics includes information on any of the following for anappliance or server 1) load; 2) numbers and types of connections, 3)resource usage, 4) resource availability, 5) number of requestsoutstanding, 6) number of requests transmitted, 7) number of clientsservicing, 8) response time information, including average andhistorical response times, 9) errors, status, performance or bandwidthof a connection, and 10) number of sessions, and states or statusthereof. In another embodiment, the metrics 530 includes information onany IP or network layer information of the appliance 200A-200N,500A-500N, or the connections of the appliance 200A-200N, 500A-500N, orof the clients and/or servers serviced by the appliance 200A-200N,500A-500N. For example, the information provided via metrics 530 mayinclude a routing table of the appliance 200A-200N, 500A-500N forperforming network address translation, such as for an SSL VPNconnection.

Via the configuration interface 425, a user may select one or moremetrics 430 from the global metrics 530 to use for load monitoring anddetermining the load 440. The appliance 200 may receive informationidentifying a user selection of one or more metrics from the globalmetrics 530. The appliance may receive a user selection of one or moreMEP based metrics 510 of a first type of appliance. The appliance mayreceive a user selection of one or more NMP based metrics 520 of asecond type of appliance. The appliance may also receive a userselection of one or more NMP based metrics 520′ for any server or serverfarm. The user may select any combination of metrics 430 from the globalmetrics 530 to configure the appliance 200 to perform load balancing ofheterogeneous devices according to the user selected metrics.

In one embodiment, the appliance 200 uses appliance established metricsin combination with any one or more of the user selected metrics 430 forload balancing. For example, the appliance 200 may collect and monitorthe number of connections, response time, bandwidth and numbers ofpackets for any appliance 200, 500 or server 106 and use these metricswith any user selected metrics for load balancing. Via the configurationinterface 425 and as also discussed in conjunction with FIGS. 4A and 4B,the appliance 200 may receive information from the user identifying,designating or establishing weights 435 and/or thresholds 437 for anyappliance established metrics and/or user selected metrics.

Referring now to FIG. 5C, an embodiment of steps of a method 550 forperforming global load balancing among heterogeneous devices isdepicted. In brief overview, at step 555, the appliance 200 identifies aplurality of metrics from heterogenous devices to use for load balancingby the appliance. At step 560, the appliance 200 obtains metrics fromone or more homogenous appliances 200A-200N or appliances of the sametype as the first load balancing appliance 200. At step 565, theappliance 200 obtains metrics from heterogenous devices, such asappliances 500A-500N and/or servers 106, via a network managementprotocol, such as SNMP. At step 570, the appliance determines a load ofone or more of the plurality of appliances, servers, and/or servicemanaged by the appliance 200 based on the metrics collects at step 560and step 565. At step 575, the appliance receives a client request toaccess a service. At step 580, the appliance determines based on theload one of the appliances 200A-200N, 500A-500N or one of the servers towhich to direct the client request. At step 580, the appliance 200transmits the request to the device, appliance or service selected inaccordance with the determined load.

In further details, at step 555, the appliance 200 identifies metrics tocollect and monitor for load balancing one or more appliances 200A-200N,500A-500N, servers 106 or services 270A-270N. In one embodiment, theappliance 200 provides or identifies one or more appliance collectedmetrics 410 as described in conjunction with FIGS. 4A and 4B. Forexample, a table 410 may identify metrics collected by the appliance200. In another embodiment, the appliance 200 provides one or morepredetermined tables of appliance provided metrics 510 or 520, such asfor an appliance of Citrix, F5, Cisco, or Radware. In other embodiments,the appliances 200 identifies one or more metrics to collect via anetwork management protocol in an object or variable database, such asan MIB 417 for SNMP. In one embodiment, the appliance provides apreconfigured or preinstalled MIB 417 for a predetermined appliance200A-200N, 500A-500N, server 106 or service 270.

In some embodiments, the appliance 200 queries an appliance 200A-200N,500A-500N, server 106 or service 270 to determine available metrics tocollect and/or monitor. For example, in one embodiment, the appliance200 queries an appliance, server or service for available objectidentifiers 422A-422N. In another embodiment, the appliance 200 uses anetwork management protocol, such as SNMP, to query for theidentification of objects in a MIB 417. In yet another embodiment, auser via the configuration interface 425 identifies one or more objectidentifiers 422A-422N to collect and/or monitor from a appliance200A-200N, 500A-500N, server 106 or service 270. In some embodiments,the user via the configuration interface 425 identifies one or more ofthe global metric 530 to collect and/or monitor from any one of theheterogenous device under management.

At step 560, the appliance 200 collects and/or monitors metrics510A-510N from one or more appliances 200A-200N via a MEP protocol 540.In some embodiments, the appliances 200A-200N are of the same type orhomogenous with the appliance 200. In one embodiment, the appliance 200collects and/or monitors metrics 510 established, determined orotherwise selected by the appliance. In another embodiment, theappliance 200 collects and/or monitors metrics 510 established,determined or otherwise selected by a user. In some embodiments, theappliance 200 uses a first type or version of the MEP protocol 540 tocollect metrics from a first appliance 200A and a second type or versionof the MEP protocol 540′ to collect metrics from a second appliance200N.

One or more load monitors or monitoring agents 405A-405N of theappliance 200 may be configured, constructed or implemented to identify,collect and/or monitor metrics via MEP protocol 540 from one or moreappliances 200A-200N. A first load monitor 405A may collect and monitormetric values from a first appliance 200A. A second load monitor 405Nmay collect and monitor metric values from a second appliance 200N. Athird load monitor 405 may collect and monitor metric values from thefirst and second appliances 200A-200N. A load monitor 405A-405N maycollect and/or monitor metrics on any type of schedule or predeterminedfrequency. In some embodiments, the load monitor 405 collects metricsresponsive to the detection of an event.

At step 565, the appliance 200 collects and/or monitors metrics520A-520N′ from one or more appliances 500A-500N, servers or a serverfarm any type and form of network management protocol. In someembodiments, the appliances 500A-500N are a different type orheterogeneous with the appliance 200. In other embodiments, one or moreof the appliances 500A-500N are of a different type or heterogenous withone or more of the other appliances 500A-500N. In one embodiment, theappliance 200 collects and/or monitors metrics 520 established,determined or otherwise selected by the appliance. In anotherembodiment, the appliance 200 collects and/or monitors metrics 520established, determined or otherwise selected by a user. In someembodiments, the appliance 200 uses a first type or version of a networkmanagement protocol, such as SNMP, to collect metrics from a firstappliance 500A and a second type or version of a network managementprotocol, SNMP or CIMS, to collect metrics from a second appliance 500N.

One or more load monitors or monitoring agents 405A-405N of theappliance 200 may be configured, constructed or implemented to identify,collect and/or monitor metrics via a network management protocol fromone or more appliances 500A-500N. A first load monitor 405A may collectand monitor metric values from a first appliance 500A. A second loadmonitor 405N may collect and monitor metric values from a secondappliance 500N. A third load monitor 405 may collect and monitor metricvalues from a server 106 or server farm 38. In other embodiments,multiple monitors 405A-405N may collect and/or monitor metrics from aplurality of appliances 500A-500N and/or servers 106. A load monitor405A-405N may collect and/or monitor any of the metrics 520A-520N on anytype of schedule or predetermined frequency. In some embodiments, theload monitor 405 collects metrics 520A-520N′ responsive to the detectionof an event.

At step 570, the appliance determines a load for each of the one or moreappliances 200A-200N, 500A-500N, servers, server farm or services. Insome embodiments, a vServer 275 determines the load 440 for each service270 via metric information collected and monitored by a load monitor405. In another embodiment, the load monitor 405 determines the load 440for appliance, server or service being monitored.

The appliance 200, vServer 275 and/or load monitor 405 may determine theload 440 using a user selected metric 430 weighted by a user designatedweight 435. In some embodiments, the appliance 200 and/or load monitor405 determines the load 440 using a plurality of user selected metrics430 weighted by user designated weights 435. In yet another embodiment,the appliance 200 and/or load monitor 405 determines the load using auser selected metric 430 and user identified weight 435 and an applianceestablished metric 410 and an appliance established weight 435. Infurther embodiments, the appliance 200 determines the load 440 bysumming a weighted load for each metric. For the embodiment of multiplemonitors 405A-405N per service 270, the appliance 200 may determine theload for an appliance, server or service by assigning a weight to eachmonitor and computing weighted load across all the monitors 405. In yetanother embodiment, the appliance may determine the load for anappliance, server or service by assigning a weight to each of theappliance, service or service.

In some embodiments, a load monitor 405 determines that a metric 530 foran appliance, server or service has reached or exceeded a threshold 437.In other embodiments, a load monitor 405 determines that a metric 530for an appliance, server or service is within a threshold 437. In oneembodiment, the load monitor 405 uses an appliance established orprovided threshold for a metric 530. In another embodiment, the loadmonitor 405 uses a user specified or configured threshold 437.

At step 575, the appliance 200 receives a request from a client toaccess a service. In one embodiment, a virtual server or vServer 275 ofthe appliance 200 intercepts or otherwise receives a request from theclient. In some embodiments, the virtual server 275 transparentlyintercepts the client's request to a service 270 or server 106. In otherembodiments, a client 102 transmits the request to the vServer 275. Inanother embodiment, the vServer 275 determines from the request that therequest is for one or more services under management by the appliance200. In one embodiment, the vServer 275 intercepts or receives therequest via a SSL VPN connection between the client and the appliance200. At step 580, the appliance 200 determines which of the appliances200A-200N, servers 106 or services 270A-270N to direct the clientrequest based on determination of the load 440 for each of theappliances 200A-200N, servers 106 or services 270A-270N. In oneembodiment, the vServer 275 directs the request responsive to one ormore load monitors 405. In some embodiments, a vServer 275 directs,forwards or otherwise transmits the request to an appliance 200A-200N,500A-500N, server or service with the least or smallest load. In oneembodiment, the vServer 275 directs, forwards or otherwise transmits therequest to an appliance 200A-200N, 500A-500N, server or service with oneof the lower determined loads. In some embodiments, the vServer 275directs, forwards or otherwise transmits the request to the s anappliance 200A-200N, 500A-500N, server or service previously handlingrequests from the client 102. In one embodiment, the vServer 275transmits the request to the previously used an appliance 200A-200N,500A-500N, server or service if the load for the appliance 200A-200N,500A-500N, server or service is within a predetermined threshold. Insome embodiments, the vServer 275 transmits the request to the firstavailable an appliance 200A-200N, 500A-500N, server or service in a listwith a determined load within a predetermined threshold.

In another embodiment, a vServer 275 directs, forwards or otherwisetransmits the request to an appliance 200A-200N, 500A-500N, server orservice using a round robin technique, or weighted round robin. In yetanother embodiment, the vServer 275 directs the request to an appliance200A-200N, 500A-500N, server or service based on one or more metrics,such as appliance collected metrics 410 or device provided metrics 420.For example, in some embodiments, the vServer 275 directs the request toan appliance 200A-200N, 500A-500N, server or service based on one ormore of the following: least response or round trip time, least numberof connections, least number of packets, and least used bandwidth. Inyet other embodiments, the vServer 275 directs the request to anappliance 200A-200N, 500A-500N, server or service based on one or moredevice provided metrics 530, such as CPU, memory and disk resourceusage. In another example, the vServer 275 directs the request to anappliance 200A-200N, 500A-500N, server or service based on resourceusage on or of an appliance 200A-200N, 500A-500N, server or service.

In some embodiments, a vServer 275 may not direct a request to anappliance 200A-200N, 500A-500N, server or service in which a metric forthe service 270 has exceeded a threshold 437, such as a user configuredthreshold 437. In other embodiments, a vServer 275 may not direct to arequest to an appliance 200A-200N, 500A-500N, server or service if morethan one threshold 437 of the metrics 530 for the appliance 200A-200N,500A-500N, server or service has been exceeded. In yet anotherembodiment, a vServer 275 may direct a request to an appliance200A-200N, 500A-500N, server or service even if a metric threshold 437has been reached or exceeded. For example, if one metric threshold 437of a plurality of thresholds 437 has been exceeded, then the vServer 275may still direct the request to the appliance 200A-200N, 500A-500N,server or service if the other metric thresholds have not been reached.

In still other embodiments, the appliance 200 may determine from loadmonitoring that a metric of a first GSLB vServer 275A has reached athreshold 437. In response to the determination, the appliance 200 mayspillover management of the appliances 200A-200N, 500A-500N, servers orservices to a second GSLB virtual server, or vServer 275B. In oneembodiment, the second virtual server 275B may be a backup GSLB server.In some embodiments, the second GSLB virtual server 275B is establishedin response to detecting the first GSLB virtual server 275A has reachedone or more thresholds. In another embodiment, the second GSLB virtualserver 275B may be established and running on the appliance 200.

At step 580, the appliance 200 transmits the client request to theappliance 200A-200N, 500A-500N, server or service identified by theappliance at 585. In one embodiment, the appliance 200 transmits theclient request in a manner transparent to the appliance 200A-200N,500A-500N, server or service such that the request appears to have beensent from the client instead of the appliance 200. For example, theappliance 200 may act as a transparent or intercepting proxy for theclient 102. In other embodiments, the appliance 200 acts as anon-transparent proxy and transmits the request to the appliance200A-200N, 500A-500N, server or service on the client's behalf. In someembodiment, the vServer 275 transmits the request to the appliance200A-200N, 500A-500N, server or service. In other embodiments, a backupvServer 275 transmits the request to the appliance 200A-200N, 500A-500N,server or service. In yet other embodiments, a second vServer 275transmits the request to the appliance 200A-200N, 500A-500N, server orservice

Although the systems and methods of FIGS. 5A-5C are generally discussedin the context of global server load balancing, these systems andmethods may be used for local load balancing. The appliance 200 may usemetrics obtained from heterogeneous devices, servers, or services usinga plurality of protocols to load balance one or more services orservers. Using the techniques described herein, the appliance 200 isconfigurable and flexible to obtain metrics from any networkresource—system, sub-system, application, service, device, etc—usingeither a metric exchange protocol supported by the appliance and/or amore general network management protocol supported by the networkresource. Additionally, the appliance 200 is configurable to allow usersto select any combination of available metrics from these heterogenousnetwork resources to perform load monitoring and load balancing of oneor more services.

F. Global Server Load Balancing Based on SSL VPN Users

Referring now to FIG. 6A, a block diagram of an embodiment of a systemfor global server load balancing across a plurality of sites based on anumber of Secure Socket Layer Virtual Private Network (SSL VPN) users isillustrated. In brief overview, a Global Server Load Balancing virtualserver (GSLB) of appliance 200/500 balances network traffic acrossmultiple appliances 200/500. Appliance 200/500A is located at site A andbalances the network traffic received from the GSLB appliance 200/500across a group of servers 106 deployed at site A. Similarly, appliance200/500B is located at site B and balances the network traffic receivedfrom the GSLB appliance 200/500 across a group of servers stationed atsite B. Site A servers, servers 106A-B, receive the network trafficbalanced by appliance 200/500A. Site B servers, servers 106C-D, receivethe network traffic balanced by appliance 200/500B.

Any of the servers at any of the sites may service any users, includingSSL VPN users. By way of example, servers 106A-D provide service to SSLVPN users 650A-N and users 660A-N, wherein N can be any number. GSLBappliance 200/500 includes a GSLB vServer 275 comprising a SSL VPN LoadBalancer or load balancing scheme 605 which load balances requests basedon SSL VPN metrics or statistics. Appliances 200/500 include LB vServers275 and SSL VPN Managers 620.

Each of the appliances at the site may have an SSL VPN Manager 620 whichidentifies and/or monitors a number of users accessing services at thesite, including a number of SSL VPN users. SSL VPN Manager 620A ofappliance 200/500A may identify users 660 and SSL VPN users 650 from thesite A. Similarly, SSL VPN Manager 620B of the appliance 200/500Bidentifies users 660 and SSL VPN users 650 from the site B. GSLBappliance 200/500 may communicate with appliances 200/500 via a numberof protocols, such as MEP 540 or SNMP protocols. GSLB 200/500 appliancemay receive from appliances 200/500 information identifying the numberof SSL VPN users 650 at each of the sites A and B. GSLB appliance200/500 may determine via SSL VPN load balancing 605 which appliance200/500 to receive an incoming request based on the number of SSL VPNusers 650 at each of the sites A and B.

In further overview, FIG. 6A depicts a GSLB appliance 200/500 loadbalancing incoming network traffic across appliances 200/500 that arepositioned at a plurality of sites. GSLB appliance 200/500 may be anytype and form of intermediary that balances network traffic across anynumber of devices on the network, such as appliances 200, appliances500, servers 106 or clients 102. GSLB appliance 200/500 may be anyappliance 200 or appliance 500 load balancing network traffic across aplurality of other appliances 200 or appliances 500. In someembodiments, GSLB appliance 200/500 is an intermediary forwardingcommunication between any number of clients 102 and any number ofappliances 200 or appliances 500. In some embodiments, GSLB appliance200/500 is an appliance 200. In other embodiments, GSLB appliance200/500 is an appliance 500. In yet further embodiments, GSLB appliance200/500 is an appliance that includes any functionality of any appliance200 and appliance 500 described in conjunction with previous figures. Inaddition to the aforementioned LB vServer 275, GSLB appliance 200/500may further comprise SSL VPN load balancing 605. In some embodiments,GSLB appliance 200/500 comprises any components or any functionality ofany embodiments of appliance 200, appliance 500, client 102 or server106. The GSLB appliance 200/500 may further comprise functionality tocommunicate with any appliance 200 or any appliance 500 via any type ofprotocol, such as MEP protocol or SNMP protocol.

GSLB vServer 275 may be any embodiment of vServer 275 described herein.The GSLB vServer 275 may further comprise any functionality to balancenetwork traffic across a plurality of appliances 200/500. GSLB vServer275 may perform global server load balancing by load balancing aplurality of appliances 200, appliances 500 or appliances 200/500. GSLBvServer 275 may also utilize any one or more of a plurality of schemesfor load balancing of the devices, such as least connection, round triptimes, round robin, least response time, least bandwidth, least networkpackets and proximity. In some embodiments, GSLB vServer 275 maycomprise a SSL VPN load balancing scheme 605 for load balancing requestsand devices based on SSL VPN user metrics. In some embodiments, the GSLBappliance may use the SSL VPN user metric or scheme 605 in combinationany one or more other load balancing algorithms, such as leastconnection, round trip times, round robin, least response time, leastbandwidth, least network packets and proximity.

SSL VPN load balancer or load balancing scheme 605 may comprises anyfunction, operations, logic or rule for load balancing based on any typeand form of statistics or metrics about SSL VPN users, such as currentnumber of SSL VPN users. The metrics or statistics may includeinformation or data on a number of SSL VPN session, a number of SSL VPNconnections and/or a number of SSL VPN users. The SSL VPN load balancer605 may be any unit, device, function, software, algorithm or acomponent of a GSLB vServer 275 that provides functionality to determineto which devices to forward a request based on SSL VPN users. SSL VPNload balancing scheme 605 may utilize information identifying SSL VPNusers on any number of sites, such as sites A and B, to determine whichdevice to forward a request received by the GSLB appliance 200/500. SSLVPN Scheme 605 may receive from the appliances 200/500 informationrelating the number of SSL VPN users on all the servers 106 loadbalanced by the appliances 200/500, and in response to the informationreceived determine which of the appliances 200/500 will receive theincoming request. The SSL VPN load balancing scheme 605 may determinewhich appliance 200/500 to forward a request received by the GSLBappliance 200/500 based on the type of connection the client 102 isrequesting or is currently connected with, such as SSL VPN connection.For example, GSLB appliance 200/500 may receive a request from a client102 which may already be using an SSL VPN session.

A site, such as sites A or B, may be any location(s) or deploymentcomprising one or more appliances 200/500 and one or more servers 106being load balanced by the one or more appliances 200/500. For example,a site may be a data center. In another example, a site may be anoffice, such as a branch office. A site may be a geographical locationin which a group of servers 106 and appliances 200/500 are located. Asite may be a plurality of geographical locations over which a group ofservers 106 and appliances 200/500 are spread out. In some embodiments,a site is a room housing a group of servers and an appliance 200/500. Inother embodiments, a site is a group of servers 106 located over anumber of areas being load balanced by an appliance 200/500. In someembodiments, a site is any group of servers 106 being load balanced byone or more appliances 200/500. A site may be one or more servers 106.

Appliances 200/500, such as appliances 200/500A or appliance 200/500Bmay be any embodiment of appliance 200 or appliance 500 describedherein. In some embodiments, an appliance 200/500 comprises an SSL VPNmanager 620. The SSL VPN manager 620 may comprise any function,operations or logic for monitoring, counting and/or gatheringinformation relating to SSL VPN connections, SSL VPN sessions or SSL VPNusers. The SSL VPN manager 620 comprises software, hardware or acombination of software and hardware. The SSL VPN manager may comprisean application, program, library, script, task, process, service, threador any form and set of executable instructions.

The SSL VPN manager 620 may obtains, establish determine or otherwiseprovides any type and form of metrics or statistics related to SSL VPNusers and/or SSL VPN sessions. In some embodiments, SSL VPN manager 620determines a count of a number of SSL VPN users accessing the site. Insome embodiments, SSL VPN manager 620 determines a count of a number ofSSL VPN users accessing servers via the appliance. In some embodiments,SSL VPN manager 620 determines a count of a number of SSL VPN on each ofthe servers managed by the appliance. In some embodiments, SSL VPNmanager 620 monitors and determines information relating SSL VPN users,SSL VPN sessions or SSL VPN connections only on the servers loadbalanced by the appliance 200/500. In yet further embodiments, SSL VPNmanager 620 maintains statistics, metrics or count of any SSL VPNsessions or any SSL VPN threads on any of the servers 106.

In some embodiments, SSL VPN manager 620 determines load balancingacross the plurality of servers 106 of the site in response to any ofthe SSL VPN user and/or session metrics or statistics. In theseembodiments, the site appliance may perform local site load balancingusing the SSL VPN user metrics. In other embodiments, SSL VPN manager620 determines load balancing across the plurality of servers 106 inresponse to the information or metrics relating the number of SSL VPNuser 650 connections and user 660 connections on any of the servers 106.

SSL VPN manager 620 may identify any users of the site, appliance or anyappliance, server or service of the site or otherwise accessed via theappliance, such as SSL VPN users 650 and users 660. SSL VPN manager 620may comprise information relating to any SSL VPN user 650 gathered bymonitoring of the network traffic of the SSL VPN user 650 whichtraverses the appliance 200/500. The SSL VPN manager 620 may compriseany information of any user within the site which appliance 200/500services. The SSL VPN manager may distinguish and determine those userswhich are SSL VPN users in comparison to users that are not accessingservices via SSL VPN. In some embodiments, the SSL VPN users are asubset of all users at the site. In some embodiments, a user mayconcurrently be both a SSL VPN user and a non-SSL VPN user. In some ofthese embodiments, the SSL VPN manager may count and consider the useras an SSL VPN user. In other embodiments, the SSL VPN manager may notcount and consider the user as an SSL VPN user.

Still referring to FIG. 6A, the users and SSL VPN users of the site aredescribed. FIG. 6A illustrates servers 106 comprising users 660 and SSLVPN users 650. Servers 106A-B are servers at the site A, load balancedby appliance 200/500A of the site A. Appliance 200/500A comprises SSLVPN manager 620A which may identify the users 660 and SSL VPN users ofthe servers at site A. Appliance 200/500B comprises SSL VPN manager 620Bwhich may identify the users 660 and SSL VPN users of the servers atsite B. In some embodiments, the appliance 200/500 has, establishes orotherwise maintains a set of users and SSL VPN users of the appliance.In some embodiments, the users and SSL VPN users of an appliance are thesame users and SSL VPN users of the servers. In other embodiments, someof the users and/or SSL VPN users of the appliance are different thansome of the users and/or SSL VPN users of the servers. In someembodiments, site A may have one or more users and/or one or more SSLVPN users in common with users and/or SSL VPN users at site B. Thenumber of users 660 and/or SSL VPN users 650 may vary at each site.

SSL VPN user 650 may be any user accessing via an SSL VPN connection orsession a resource at a site, an appliance, or any server of the site orotherwise managed by the appliance. In some embodiments, SSL VPN user650 is a user on a client 102 establishing an SSL session orcommunication via an SSL session. In other embodiments, SSL VPN user 650is a user establishing an SSL session on a server 106. In someembodiments, SSL VPN user 650 is a user establishing an SSL VPN sessionwith the appliance 200/500 or otherwise sending communicationstraversing the appliance via an SSL VPN session. In some embodiments,SSL VPN user 650 is a user from a device on a first network, such as apublic network, accessing a server 106 on a second network, such asprivate network utilizing SSL VPN. As described herein, the appliance200/500 established and manages access between networks and locations.SSL VPN user 650 may be any user using an SSL VPN session, SSL VPNconnection or any secure tunneling protocol.

User 660 may be any user accessing a resource at a site, an appliance,or any server of the site or otherwise managed by the appliance. A usermay be an SSL VPN user. A user may a user not using SSL VPN. A user maybe a user with an SSL VPN session and a non-SSL VPN session. In someembodiments, user 660 is a user on a client 102 connecting to the server106. In some embodiments, user 660 is a user of the appliance 200/500.In some embodiments, user 660 is a user opening a plurality ofconnections to the server 106. In other embodiments, user 660 is a useron the server 106 that does not utilize SSL VPN. In some embodiments,user 660 may have any number of connections on the server 106. In otherembodiments, user 660 may have any number of user sessions on the server106. User 660 may be any user using any computing device to communicatewith the server 106.

Referring now to FIG. 6B, a flow diagram of embodiments of a method forglobal server load balancing of a plurality of sites based on a numberof SSL VPN users accessing the servers is illustrated. In brief overviewof method 600, at step 605 a global server load balancing virtual server(GSLB) load balances a plurality of sites and receives a request toaccess a server. At step 610, a load balancing virtual server (LBvServer) at each of the plurality of sites load balances users accessesto servers. At step 615, a first LB vServer determines a first number ofcurrent SSL VPN users accessing servers from the first site via SSL VPNsessions and a second LB vServer determines at a second site a secondnumber of current SSL VPN users accessing servers from the second sitevia SSL VPN sessions. At step 620, the GSLB receives from the number ofcurrent SSL VPN users from the plurality of sites, such as from thefirst LB vServer and the second LB vServer. At step 625, the GSLBdetermines to forward the request to one of the sites, such as the firstLB vServer or the second LB vServer based on the current number of SSLVPN users at each site.

In further view, at step 605 a global server load balancing virtualserver (GSLB) load balances multiple sites receives a request to accessa server. GSLB, such as a GSLB appliance 200/500, may receive a requestto resolve a domain name. In some embodiments, GSLB receives a requestto establish a SSL VPN session. GSLB, such as GSLB appliance 200/500 mayreceive a request from a client 102 to access a webpage or a file on oneof the servers 106. In some embodiments, GSLB receives a request from aclient 102, a server 106 or any device on a network to access anapplication provided by a server 106. In some embodiments, GSLB receivesa request from a plurality of clients 102 to access a streaming file,such as an audio or a video file stored on a server 106. In someembodiments, GSLB receives a request from a user on a client 102 to login to an email service provided by the server 106. The request receivedby the GSLB may be any request to access a resource or a service at anyserver 106. Based on the request, the GSLB load balances requests acrosssites using any load balancing scheme or algorithm, including but notlimited to one or more of the following: least response or round triptime, least number of connections, least number of packets, and leastbandwidth. In some embodiments, the GSLB load balances in accordancewith SSL VPN loading balancing scheme 605 described herein. In oneembodiment, the GSLB load balances across sites based on a number of SSLVPN users at each site.

At step 610, one or more load balancing virtual servers (LB vServers) ateach of the sites load balances any user accesses accessing servers 106.In some embodiments, a load balancing virtual server of a particularsite, such as a LB vServer 275A of appliance 200/500A, load balancestraffic from users requesting access to servers 106 of the particularsite, such as site A. In some embodiments, a plurality of load balancingvirtual servers balance the network traffic across a plurality of groupsof servers 106, each of the groups corresponding to a site load balancedby one of the load balancing virtual servers. In other embodiments, eachof load balancing virtual servers corresponding to each of the sitesbalances network traffic across any number of servers 106 within each ofthe particular sites load balanced by the load balancing virtualservers. In some embodiments, a first LB vServer at a first site loadbalances network traffic across a first group of servers 106 at a firstsite. A second LB vServer at a second site may load balance networktraffic across a second group of servers 106 at a second site.Similarly, a third LB vServer at a third site may load balance a networktraffic across a third group of servers 106 at a third site. In someembodiments, any of the LB vServers are performing local site loadbalancing while the GSLB is load balancing requests across sites.

At step 615, any LB vServer of the first site determines a first numberof current SSL VPN users accessing servers from the first site and anyLB vServer of the second site determines a second number of current SSLVPN users accessing servers from the second site. In some embodiments, afirst LB vServer determines a first number of current SSL VPN usersaccessing servers from the first site via one or more SSL VPN sessions.Similarly, a second LB vServer may determine a second number of currentSSL VPN users accessing servers from the second site via one or more SSLVPN sessions. In other embodiments, any LB vServer of the plurality ofLB vServers at the first site determines a first number of current SSLVPN users accessing servers from the first site via SSL VPN sessions.Likewise, any LB vServer of the plurality of LB vServers at the secondsite may determine a first number of current SSL VPN users accessingservers from the second site via SSL VPN sessions.

In yet further embodiments, one or more LB vServers at the first sitedetermine a first number of current SSL VPN connections connected to theservers at the first site. One or more LB vServers at the second sitemay determine a first number of current SSL VPN connections connected tothe servers at the second site. In still further embodiments, one ormore LB vServers at the first site determine a first number of currentSSL VPN users having sessions at servers 106. Similarly, one or more LBvServers at the second site may determine a second number of current SSLVPN users having sessions at servers 106. In some embodiments, the firstnumber is the number of current SSL VPN sessions accessing the serversat the first site. The second number may be the number of current SSLVPN sessions accessing the servers at the second site. In otherembodiments, the first number is the number of users currently connectedto the servers using SSL VPN connections at the first site. The secondnumber may be the number of users currently connected to the serversusing SSL VPN connections at the second site

Any of the LB vServers or appliances may report the number of SSL VPNusers based on any type and form of statistics on the SSL VPN users. Insome embodiments, the number of SSL VPN users is provided as an averageover any time periods. In some embodiments, the number of SSL VPN usersis provides as peak number of SSL VPN users. In other embodiments, thenumber of SSL VPN users is provides as a range. In another embodiments,the number of SSL VPN users is provides as well as the number of SSL VPNsessions. For example, a single SSL VPN user may have multiple SSL VPNsessions. In still further embodiments, the first number is any numberof users using SSL VPN to connect to one or more servers at the firstsite within a past predetermined time period. In some embodiments, thesecond number is any number of users using SSL VPN to connect to one ormore servers at the second site within a past predetermined time period.The past predetermined time period may be any time period such as theprior minute, the prior hour, the prior day, the prior month or theprior year from the moment of determination of the first number.

At step 620, the GSLB receives from any of the appliances at each of themultiple sites information on the number of SSL VPN users, and/or anymetrics or statistics thereof. In some embodiment, the GSLB receivesfrom any of the LB vServers at the first site a first number of currentSSL VPN users and from any of the LB vServers from the second site asecond number of current SSL VPN users. GSLB, such as the GSLB appliance200/500, may receive the first number or the second number via MEP 540protocol. In some embodiments, GSLB receives the first number or thesecond number via SNMP protocol. GSLB may receive the first number orthe second number via any communication means and via any communicationscheme or communication protocol. The GSLB may receive the SSL VPN userinformation on a predetermined frequency. The GSLB may request the SSLVPN user information on a predetermined frequency. The GSLB may receivethe SSL VPN user information upon changes to the information. The GSLBappliance may receive the information from an appliance of a first siteat a different time or frequency than an appliance of second site. TheGSLB appliance may receive the information from an appliance of a firstsite at a same or concurrent time or frequency as an appliance of secondsite. The GSLB appliance may receive the information from an applianceof a second site subsequent to an appliance of the first site.

At step 625, GSLB performs load balancing of client access across thesites based on the received SSL VPN user information using the SSL VPNload balancing scheme 605 alone or in combination with any loadbalancing algorithm of the appliance. The GSLB determines to forward therequest to any one the LB vServers at the first site or any one of theLB vServers at the second site based on the number of SSL VPN users ateach site. GSLB may determine to forward the request to one of the firstLB vServer or the second LB vServer based on the first number of currentSSL VPN users and the second number of current SSL VPN users. In someembodiments, GSLB determines to forward the request received by the GSLBto the first LB vServer of the first site upon determining that thenumber of the SSL VPN users currently connected to the servers of thefirst site is smaller than the number of the SSL VPN users currentlyconnected to the servers of the second site. In other embodiments, GSLBdetermines to forward the request to the first LB vServer of the firstsite upon determining that the number of the SSL VPN users currentlyconnected to the servers of the first site is greater than the number ofthe SSL VPN users currently connected to the servers of the second site.In further embodiments, GSLB determines to forward the request to thesecond LB vServer of the second site upon determining that the number ofthe SSL VPN user sessions currently active on the servers of the firstsite is smaller than the number of SSL VPN user sessions currentlyactive on the servers of the second site. In some embodiments, GSLBdetermines to forward the request to the second LB vServer upondetermining that the number of the SSL VPN connections currentlyconnected to the servers of the first site is smaller than the number ofthe SSL VPN connections currently connected to the servers of the secondsite. GSLB may determine to forward the request to either the first LBvServer of the first site or the second LB vServer of the second site.In some embodiments, the GSLB appliance determines one or morethresholds of the number of SSL VPN users allowed or desired for a sitehas been reached and excluding the site from load balancing until thesite no longer exceeds the threshold. In some embodiments, even though athreshold has been reached at a site, the GSLB forwards a request to thesite for client, user or site persistence.

What is claimed is:
 1. A method of load balancing based on a number ofSecure Socket Layer Virtual Private Network (SSL VPN) users, the methodcomprising: (a) receiving, by a device, a first number of Secure SocketLayer Virtual Private Network (SSL VPN) users of a first site of aplurality of sites distinguished from users of the first site that arenot SSL VPN users; (b) receiving, by the device, a second number of SSLVPN users of a second site distinguished from users of the second siteof the plurality of sites that are not SSL VPN users; and (c) loadbalancing, by the device, requests of clients among the first site andthe second site based on the first number of SSL VPN users and thesecond number of SSL VPN users.
 2. The method of claim 1, wherein step(a) further comprises receiving, by the device, the first number of SSLVPN users from a second device load balancing a plurality of servers atthe first site.
 3. The method of claim 1, wherein step (b) furthercomprises receiving, by the device, the second number of SSL VPN usersfrom a second device load balancing a plurality of servers at the secondsite.
 4. The method of claim 1, wherein step (a) further comprisesreceiving, by the device, the first number of SSL VPN users accessingservers at the first site via a SSL VPN session.
 5. The method of claim1, wherein step (b) further comprises receiving, by the device, thesecond number of SSL VPN users accessing servers at the second site viaa SSL VPN session.
 6. The method of claim 1, wherein each of the firstnumber of current SSL VPN users and the second number of current SSL VPNusers comprises an average number of SSL VPN users over a predeterminedtime period.
 7. The method of claim 1, wherein each of the first numberof current SSL VPN users and the second number of current SSL VPN userscomprises a peak number of SSL VPN users.
 8. The method of claim 1,wherein step (c) further comprises load balancing requests of clientsfor accessing via an SSL VPN session a server at one of the plurality ofsites.
 9. The method of claim 1, wherein load balancing furthercomprises global server load balancing by resolving domain names tointernet protocol addresses of servers at the plurality of sites. 10.The method of claim 1, wherein step (c) further comprises determining,by the device, that a threshold of a maximum number of SSL VPN users forthe first site has been reached and responsive to the determination,forwarding requests to the second site.
 11. A system for load balancingbased on a number of Secure Socket Layer Virtual Private Network (SSLVPN) users, the system comprising: a device configured to receive: afirst number of Secure Socket Layer Virtual Private Network (SSL VPN)users of a first site of a plurality of sites distinguished from usersof the first site that are not SSL VPN users and a second number of SSLVPN users of a second site distinguished from users of the second siteof the plurality of sites that are not SSL VPN users; and a virtualserver of the device configured to load balances requests of clientsamong the first site and the second site based on the first number ofSSL VPN users and the second number of SSL VPN users.
 12. The system ofclaim 11, wherein the device is further configured to receive the firstnumber of SSL VPN users from a second device load balancing a pluralityof servers at the first site.
 13. The system of claim 11, wherein thedevice is further configured to receive the second number of SSL VPNusers from a second device load balancing a plurality of servers at thesecond site.
 14. The system of claim 11, wherein the device is furtherconfigured to receive the first number of SSL VPN users accessingservers at the first site via a SSL VPN session.
 15. The system of claim11, wherein the device is further configured to receive second number ofSSL VPN users accessing servers at the second site via a SSL VPNsession.
 16. The system of claim 11, wherein each of the first number ofcurrent SSL VPN users and the second number of current SSL VPN userscomprises an average number of SSL VPN users over a predetermined timeperiod.
 17. The system of claim 11, wherein each of the first number ofcurrent SSL VPN users and the second number of current SSL VPN userscomprises a peak number of SSL VPN users.
 18. The system of claim 11,wherein the virtual server is further configured to load balancerequests of clients for accessing via an SSL VPN session a server at oneof the plurality of sites.
 19. The system of claim 11, wherein thevirtual server is further configured to provide load balancingcomprising global server load balancing by resolving domain names tointernet protocol addresses of servers at the plurality of sites. 20.The system of claim 11, wherein the virtual server is further configuredto determine that a threshold of a maximum number of SSL VPN users forthe first site has been reached and responsive to the determination,forward requests to the second site.